Rotating electrical machine

ABSTRACT

A rotating electrical machine includes a magnetic field-producing unit equipped with a magnet unit including a plurality of magnetic poles, and an armature which includes a multi-phase armature winding. The armature winding has conductor portions which are arranged at a given interval away from each other in a circumferential direction. The armature is designed to have conductor-to-conductor members arranged between the conductor portions in the circumferential direction. The armature may alternatively be designed not to have the conductor-to-conductor members disposed between the conductor portions in the circumferential direction. The magnet unit is magnetically oriented to have an easy axis of magnetization which is directed in a region close to a d-axis that is a center of a magnetic pole to be more parallel to the d-axis than that in a region close to a q-axis that is a boundary between magnetic poles.

CROSS REFERENCE TO RELATED DOCUMENTS

The present application claims the benefit of priority of JapanesePatent Application Nos. 2017-255056 filed on Dec. 28, 2017, 2017-255057filed on Dec. 28, 2017, 2017-2555058 filed on Dec. 28, 2017, 2017-255059filed on Dec. 28, 2017, 2017-255061 filed on Dec. 28, 2017, 2017-255062filed on Dec. 28, 2017, 2017-255063 filed on Dec. 28, 2017, 2017-255068filed on Dec. 28, 2017, 2017-255070 filed on Dec. 28, 2017, and2018-164840 filed on Sep. 3, 2018.

TECHNICAL FIELD

This disclosure generally relates to a rotating electrical machine.

BACKGROUND ART

Rotating electrical machines mounted in vehicles are generally knownwhich include a rotor equipped with permanent magnets and a statorequipped with a multi-phase stator winding. Control systems for such atype of electrical rotating machines are also known which controlexcitation of the stator winding in a switching control mode.

Rotating electrical machines have a risk of electrical erosion arisingfrom current generated in a rotating shaft thereof. For instance, PatentLiterature 1 teaches a dielectric layer disposed between an outer ironcore and an inner iron core of a rotor to regulate an electrostaticcapacitance between the outer iron core and the inner iron core, therebyminimizing a risk of electrical erosion of bearings.

PRIOR ART DOCUMENT Patent Literature

-   PATENT LITERATURE 1 Japanese patent first publication No.    2016-129439

SUMMARY OF THE INVENTION

The structure taught in the above Patent Literature 1 is, however,designed to have the dielectric layer disposed between the outer ironcore and the inner iron core of the rotor, and thus is non-standard,which leads to a concern about an increase in production costs. Thereis, therefore, still room for technical improvement for eliminating therisk of electrical erosion of the bearings.

The present invention was made in view of the above problem. It is anobject to reduce a risk of electrical erosion of a bearing of a rotatingelectrical machine.

A plurality of embodiments disclosed in this application employdifferent technical measures to achieve respective objects thereof. Theobjects, features, and beneficial advantages, as discussed in thisapplication, will be apparent by referring to the following detaileddescription and accompanying drawings.

The first means is a rotating electrical machine comprising: (a) amagnetic field-producing unit equipped with a magnet unit including aplurality of magnetic poles whose magnetic polarities are arrangedalternately in a circumferential direction; and (b) an armature whichincludes a multi-phase armature winding. One of the magneticfield-producing unit and the armature is engineered as a rotor whoserotating shaft is retained by a bearing to be rotatable. The armaturewinding has conductor portions which are arranged at a given intervalaway from each other in the circumferential direction and face themagnet unit. The armature is designed to have conductor-to-conductormembers arranged between the conductor portions in the circumferentialdirection, the conductor-to-conductor members being made from a magneticmaterial which meets a relation of Wt×Bs≤Wm×Br where Wt is a width ofthe conductor-to-conductor members in the circumferential directionwithin one magnetic pole, Bs is a saturation magnetic flux density ofthe conductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris a remanent flux density in the magnet unit, or alternatively madefrom a non-magnetic material. The armature is alternatively designed notto have the conductor-to-conductor members disposed between theconductor portions in the circumferential direction. The magnet unit ismagnetically oriented to have an easy axis of magnetization, in a regionlocated closer to a d-axis that is a center of a magnetic pole, directedto be more parallel to the d-axis than that in a region located closerto a q-axis that is a boundary between magnetic poles.

The rotating electrical machine has a risk that, for example, when thearmature winding is excited or de-excited in response to a switchingoperation, a small switching time gap (i.e., switching imbalance) mayoccur, thereby resulting in distortion of magnetic flux, which leads toelectrical erosion in the bearings retaining the rotating shaft. Thedistortion of magnetic flux depends upon the inductance of the armatureand creates an electromotive force oriented in the axial direction,which results in dielectric breakdown in the bearing to develop theelectrical erosion.

In order to alleviate the above problem, the rotating electrical machinein this means works to reduce the inductance in the armature to minimizethe distortion of magnetic flux resulting from the switching time gap tocontrol electrical erosion of the bearings. Specifically, the armaturehas any one of the following structures.

(A) The armature has the conductor-to-conductor members each of which isdisposed between the conductor portions in the circumferentialdirection. As the conductor-to-conductor members, magnetic material isused which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is the saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris the remanent flux density in the magnet unit.(B) The armature has the conductor-to-conductor members each of which isdisposed between the conductor portions in the circumferentialdirection. The conductor-to-conductor members are each made of anon-magnetic material.(C) The armature has no conductor-to-conductor member disposed betweenthe conductor portions in the circumferential direction.

Use of any one of the structures (A) to (C) enables the inductance ofthe armature to be reduced. This results in a reduction in distortion ofmagnetic flux, thereby reducing the electromotive force even when thereis a switching time gap upon energization of the armature winding.

Additionally, the magnet unit is magnetically oriented to have the easyaxis of magnetization which is directed in a region close to the d-axisto be more parallel to the d-axis than that in a region close to theq-axis. This strengthens the magnet-produced magnetic flux on thed-axis, thereby resulting in a smooth change in surface magnetic flux(i.e., an increase or decrease in magnetic flux) from the q-axis to thed-axis on each magnetic pole. This minimizes a sudden voltage changearising from the switching imbalance to avoid electrical erosion.

The second means is the rotating electrical machine as set forth in thefirst means in which the magnet unit is magnetically oriented to createan arc-shaped magnet-produced magnetic path in which the easy axis ofmagnetization is directed parallel or near parallel to the d-axis in theregion close to the d-axis and also directed perpendicular or nearperpendicular to the q-axis in the region close to the q-axis.

The above structure strengthens the magnet-produced magnetic flux on thed-axis and reduces a change in magnetic flux near the q-axis. Thisrealizes the magnet unit which achieves a smooth change in surfacemagnetic flux from the q-axis to the d-axis on each magnetic pole.

The third means is the rotating electrical machine as set forth in thefirst or second means in which the magnet unit includes a plurality ofpermanent magnets which are arranged in the circumferential direction,and wherein each of the permanent magnets is shaped to have anarmature-side outer peripheral surface facing the armature and aq-axis-side outer peripheral surface facing the q-axis in thecircumferential direction, the stator-side outer peripheral surface andthe q-axis-side outer peripheral surface functioning as magnetic fluxinput and output surfaces that are magnetic flux acting surfaces intoand from which magnetic flux flows, and in which the magnetic path iscreated to connect between the stator-side outer peripheral surface andthe q-axis-side outer peripheral surface.

The above structure strengthens the magnet-produced magnetic flux on thed-axis and reduces a change in magnetic flux near the q-axis. Thisrealizes the magnet unit which achieves a smooth change in surfacemagnetic flux from the q-axis to the d-axis on each magnetic pole.

The fourth means is the rotating electrical machine as set forth in thefirst or second means, in which the magnet unit is made of a ring-shapedmagnet that is a circular ring-shaped permanent magnet, and in which thering-shaped magnet has defined therein an arc-shaped magnet-producedmagnetic path in which a magnetic orientation is directed in the radialdirection on the d-axis of each magnetic pole and a magnetic orientationis directed in the circumferential direction on the q-axis between themagnetic poles.

The above structure strengthens the magnet-produced magnetic flux on thed-axis and reduces a change in magnetic flux near the q-axis. Thisrealizes the magnet unit which achieves a smooth change in surfacemagnetic flux from the q-axis to the d-axis on each magnetic pole.

The fifth means is the rotating electrical machine as set forth in anyone of the first t fourth means, wherein the magnetic field-producingunit has a skew structure in which the magnetic poles of the magnet unitwhich are arranged in an axial direction of the rotating shaft andoffset from each other in the circumferential direction, and wherein askew amount from a magnetic pole center line of each of the magneticpoles of the magnet unit in a first circumferential direction isidentical with that in a second circumferential direction opposite thefirst circumferential direction.

The structure in which the magnetic field-producing unit is skewed isexpected to offer an effect of reducing torque ripple, but has a concernabout electrical erosion of the bearings arising from imbalance ofmagnetic fluxes in the axial direction. The above structure is designedto have the equal skew amounts in the first and second circumferentialdirections from the energized phase center line extending in the axialdirection, thereby cancelling electrical currents flowing in the axialdirection. This minimizes a risk of electrical erosion of the bearings.

The structure in which the skew amounts from the magnetic pole centerline in the first circumferential direction and the secondcircumferential direction are equal to each other is expected to beimplemented by one of the following structures.

The structure in FIG. 36(a) that is a skew structure in which locationsof the magnets 91 in the circumferential direction are misaligned to bestepwise in the axial direction has two first portions B1 and a secondportion B2. The first portions B1 are different in circumferentiallocation from the second portion B2. In each of the first portions B1,the circumferential location of the magnet 91 is offset from themagnetic pole center line LA in the first circumferential direction. Inthe second portion B2, the circumferential location of the magnet 91 isoffset from the magnetic pole center line LA in the secondcircumferential direction. The skew amount L1 from the magnetic polecenter line LA in the first circumferential direction is identical withthe skew amount L2 from the magnetic pole center line LA in the secondcircumferential direction opposite the first circumferential direction.

The structure in FIG. 36(b) that is a skew structure in which acircumferential location of each of the magnets 91 is changed obliquelyin the axial direction. The structure has a first portion B11 and asecond portion B12. Directions in which the first portion B11 and thesecond portion B12 are inclined are oriented to be different from eachother relative to the axial direction. The first portion B11 and thesecond portion B12 are symmetric with respect to an axial boundary lineof the first and second portions B11 and B12. Each of the first andsecond portions B11 and B12 has a magnet unit center line LB extendingobliquely in a skew direction. The magnet unit center lines LB of thefirst and second portions B11 and B12 intersect with the magnetic polecenter line LA at the axial center positions P1 and P2, respectively.

The sixth means is the rotating electrical machine as set forth in anyone of the first to fifth means, wherein the armature has a skewstructure in which conductor locations of the armature winding for eachphase in the axial direction of the rotating shaft are offset in thecircumferential direction, and wherein a skew amount of each of phasewindings of the armature winding in a first circumferential directionfrom an energized phase center line extending in the axial direction isidentical with that in a second circumferential direction opposite thefirst circumferential direction.

The structure in which the armature is skewed is expected to offer aneffect of reducing torque ripple, but has a concern about electricalerosion of the bearings arising from promoted unbalance of magneticfluxes in the axial direction. The above structure is designed to havethe skew amounts by which the phase windings of the armature winding areskewed in the first and second circumferential directions from theenergized phase center line extending in the axial direction and whichare equal to each other, thereby cancelling electrical currents flowingin the axial direction. This minimizes a risk of electrical erosion ofthe bearings.

The structure in which the skew amounts from the energized phase centerline in the first circumferential direction and the secondcircumferential direction are equal to each other is expected to beimplemented by one of the following structures. Note that skewing thearmature winding requires the conductors to be continuously connectedtogether. A skew structure in which locations of the conductors of thearmature winding for each phase are changed obliquely in thecircumferential direction may, therefore, be used.

In the structure illustrated in FIG. 37(a) which is designed as a skewstructure in which each of the conductors 82 has a magnet-facing portion(i.e., a coil side) which is bent or turned back, the conductor 82includes a first section C1 and a second section C2 which are differentin inclined orientation of the conductor 82 from each other in the axialdirection. The first and second sections C1 and C2 are verticallysymmetric with each other with respect to the center point intermediatebetween the first and second sections C1 and C2 in the axial direction.The first and second sections C1 and C2 have centers P11 and P12 ofaxial lengths thereof which intersect with the energized phase centerline LC.

In the structure illustrated in FIG. 37(b) which is designed as a skewstructure in which each of the conductors 82 has a magnet-facing portion(i.e., a coil side) which is not turned back, the conductors 82 that aresame phase conductors of radially outer and inner layers of the statorwinding 51 are skewed in opposite directions. The conductor 82 of eachof the outer and inner layers has an axial center P13 intersecting withthe energized phase center line LC.

The seventh means is the rotating electrical machine as set forth in anyone of the first to sixth means, wherein the rotating shaft is retainedby the plurality of bearings to be rotatable, and wherein each of thebearings is offset from an axial center of one of the magneticfield-producing unit and the armature which works as the rotor to one ofopposed ends thereof in the axial direction.

The above structure is designed to have the bearings which retain therotating shaft and the rotor to be rotatable and are located away fromthe axial center of the rotor toward one of the ends of the rotoropposed to each other in the axial direction thereof, thereby minimizinga risk of electrical erosion as compared with a case where a pluralityof bearings are arranged outside axial ends of a rotor. In other words,in the structure wherein the rotor has ends retained by the bearings,generation of a high-frequency magnetic flux results in creation of aclosed circuit extending through the magnetic field-producing unit, thearmature, and the bearings (which are arranged axially outside therotor). This leads to a risk that the axial current may result inelectrical erosion in the bearings. In contrast, the rotor is retainedby the plurality of bearings in the cantilever form, so that the aboveclosed circuit does not occur, thereby minimizing the electrical erosionin the bearings.

The eighth means is the rotating electrical machine as set forth in theseventh means, wherein the rotating electrical machine is engineered asan outer-rotor type rotating electrical machine in which one of themagnetic field-producing unit and the armature which works as the rotoris arranged on a radially outer side, wherein the magneticfield-producing unit includes a magnet holder which retains the magnetunit, and wherein the magnet holder has an overhang which extends in aradial direction of the magnetic field-producing unit, the overhangbeing equipped with a contact avoider which extends in the axialdirection and avoids a physical contact with the armature.

The above structure has the overhang which extends in the radialdirection of the magnetic field-producing unit in the magnet holder andwhich is equipped with the contact avoider which axially extends toavoid physical contact with the armature. This enables a closed circuitthrough which the axial current flows through the magnet holder to belengthened to increase the resistance thereof. This minimizes the riskof electrical erosion of the bearings.

The contact avoider may be disposed to eliminate a physical contact of,for example, the armature with the coil ends of the armature winding.

The ninth means is the rotating electrical machine as set forth in theseventh or eighth means, wherein the rotating electrical machine isengineered as an outer-rotor type rotating electrical machine in whichone of the magnetic field-producing unit and the armature which works asthe rotor is arranged on a radially outer side, further comprising abearing retainer which surrounds the rotating shaft and retains thebearings, a housing disposed to surround the magnetic field-producingunit and the armature, and an armature holder which is disposed radiallyinside the armature to retain the armature, and wherein the bearingretainer is secured to a first end of the housing which is opposed to asecond end of the housing through the magnetic field-producing unit inthe axial direction, and the second end of the housing and the armatureholder are joined together.

The above arrangements properly achieve the structure in which thebearings are located only on one end of the length of the rotatingshaft. Additionally, the armature holder is connected to the rotatingshaft through the housing, so that the armature holder is locatedelectrically away from the rotating shaft. This also minimizes the riskof electrical erosion of the bearings.

For instance, in a case where an electrical device is arranged inconnection with the rotating shaft, the electrical device may generateelectromagnetic noise in the axial direction due to switchingdistortion. In this case, no potential difference occurs betweenbearings disposed only on an axial one side of the electrical device(e.g., two conductive bearings joined only to the axial one side),thereby minimizing electrical erosion of the bearings.

The tenth means is the rotating electrical machine as set forth in anyone of the seventh to ninth means, wherein the bearings have anon-conductive grease.

The one-side layout of the bearings in the rotating electrical machinein this means decreases the axial voltage applied to the bearings andalso decreases the potential difference between the magneticfield-producing unit and the armature. A decrease in the potentialdifference applied to the bearings is, thus, achieved without use ofconductive grease in the bearings. The conductive grease usuallycontains fine particles such as carbon particles, thus leading to a riskof generation of acoustic noise. In order to alleviate the aboveproblem, a non-conductive grease is used for the bearings to minimizethe acoustic noise in the bearings.

For instance, in a case where the rotating electrical machine is usedwith an electrical vehicle, it is usually required to take measuresagainst the acoustic noise. The above structure is capable of properlytaking such a measure.

The eleventh means is the rotating electrical machine as set forth inany one of the first to tenth means, wherein the armature includes aring-shaped base member which is disposed integrally with the armaturewinding and secured to an armature holder, and wherein the armaturewinding is covered with a molding material along with the base member.

Misalignment of the armature winding of the armature may lead to anerror in energization of the armature winding depending upon switchingoperation, which results in concern about electrical erosion of thebearings. For instance, misalignment of the conductors in thecircumferential direction which arises from lost shape of the armaturewinding may result in distortion of magnetic flux, thus leading toelectrical erosion of the bearings. For example, Japanese patent firstpublication No. H6-70522 discloses a core-less rotating electricalmachine which is equipped with a cup-shaped armature winding. Use ofsuch a cup-shaped armature winding leads to a risk that the shape of thearmature winding may be lost due to physical vibration, therebyresulting in misalignment of the conductors because the armature windinghas a complicated structure and does not have an armature core.

The rotating electrical machine in this means is designed to have one ofthe above structures (A), (B), and (C) and also have or not haveconductor-to-conductor members (i.e., protrusions or toothed portions)which are disposed in the circumferential direction between theconductors of the armature winding and too small in size for themagnet-produced magnetic flux in the magnetic field-producing unit.This, therefore, leads to a concern about misalignment of the armaturewinding, especially, in the structure (C) in which theconductor-to-conductor members are not disposed between the conductorsin the circumferential direction.

However, in this means, the armature winding is disposed integrally withthe ring-shaped base member secured to the armature holder of thearmature. The armature winding is covered with the molding materialalong with the base member, thereby minimizing the occurrence ofmisalignment of the armature winding to eliminate a locational shift ofthe armature winding in the circumferential direction. This eliminates arisk of distortion of magnetic flux arising from the misalignment of thearmature winding and resulting electrical erosion of the bearings.

The twelfth means is the rotating electrical machine as set forth in theeleventh means, wherein the base member is arranged radially inside oroutside the armature winding on an opposite side of the armature windingto the magnet unit, and wherein the base member has a surface whichfaces the armature winding and on which concavities and convexities areformed successively in at least one of the circumferential direction andthe axial direction to define recesses filled with the molding material.

The above structure is equipped with the base member having the surfacewhich faces the armature winding (i.e., the magnet unit) and on whichthe concavities and the convexities are formed successively in at leastone of the circumferential direction and the axial direction to definerecesses filled with the molding material. In this case, the moldingmaterial exists intermittently between the armature winding and the basemember, thereby minimizing a positional shift of the molding materialfrom the base member. This minimizes a risk of misalignment of thearmature winding.

When the concavities and convexities are arranged successively on thebase member in the axial direction thereof, it minimizes misalignment ofthe armature winding in the axial direction. Alternatively, when theconcavities and convexities are arranged successively on the base memberin the circumferential direction thereof, it minimizes misalignment ofthe armature winding in the circumferential direction.

The thirteenth means is the rotating electrical machine as set forth inthe eleventh or twelfth means, wherein the base member is designed as anarmature core made of a plurality of steel plates stacked on each otherin the axial direction of the rotating shaft, and wherein each of thesteel plates has an end which faces the armature winding and has across-section tapered in a thickness-wise direction thereof.

In a case where the base member is made of a stack of steel plates asthe armature core, it has a concern about generation of eddy current inthe steel plates when subjected to a strong magnetic field. Such aconcern will usually be strong on the ends of the steel plates close tothe armature winding. The above structure in which the steel plates havethe tapered ends close to the armature winding, however, minimizes thegeneration of eddy current.

The fourteenth means is the rotating electrical machine as set forth inany one of the eleventh to thirteenth means, wherein the base member isimplemented by an armature core made from a conductive material, andwherein an insulating layer is disposed between the armature winding andthe armature core.

The above structure is capable of blocking a flow of electrical currentarising from generation of magnetic field exerted by the armaturewinding on the armature core, thereby minimizing a risk of electricalerosion.

The fifteenth means is the rotating electrical machine as set forth inany one of the eleventh to fourteenth means, wherein the base member hasholes which extend in the axial direction of the rotating shaft and arefilled with the molding material.

The above structure has the molding material which covers the armaturewinding along with the base member. The molding material is disposedpartially inside the holes of the base member, so that the moldingmaterial is held from being moved in the circumferential, radial, andaxial directions. This minimizes a risk of misalignment of the armaturewinding.

In a case where the base member is designed as the armature core, itwill cause the holes to be located away from the armature winding in theradial direction, thereby reducing adverse effects on the magneticcircuit, which ensures the stability in operation of the rotatingelectrical machine.

In a case here the base member made of a stack of steel plates isdesigned as the armature core, small burrs of the steel plates usuallymake irregularities on peripheral surfaces of the holes. The moldingmaterial enters the irregularities, which function as anchors to holdthe armature winding from being misaligned.

The sixteenth means is the rotating electrical machine as set forth inany one of the eleventh to fifteenth means, wherein the armature windingis covered with the molding material except portions in an axial and aradial directions thereof.

In the above structure, the armature winding has portions exposedoutside the molding material without being covered with the moldingmaterial. Such a structure, as described above, has an effect ofminimizing the misalignment using the molding material and also enhancescooling ability of the exposed portions uncovered with the moldingmaterial.

The seventeenth means is the rotating electrical machine as set forth inany one of the eleventh to sixteenth means, wherein the armature holderis made from carbon fiber reinforced plastic.

The armature holder which retains the base member is made from carbonfiber reinforced plastic, thereby reducing electrical discharge to thearmature holder to minimize the occurrence of electrical erosion.

The eighteenth means is the rotating electrical machine, as set forth inany one of the first to seventeenth means, which further comprises apower converter which includes switches and is electrically connected tothe armature winding, and a controller which controls on-off operationsof the switches to energize the armature winding. The controller sets aswitching frequency for the switches in a low current range in which alower electrical current flows through the armature winding to be higherthan that in a high current range which is higher in electrical currentthan the low current range and in which a higher electrical currentflows through the armature winding.

The rotating electrical machine which has one of the above describedstructures (A) to (C) is capable of reducing the inductance in thearmature.

The reduction in inductance usually results in a decrease in electricaltime constant in the rotating electrical machine. This leads to a riskthat a ripple of current flowing through the armature winding may beincreased, thereby resulting in the deterioration in ease of control ofthe current flowing through the armature winding. The adverse effects ofthe above deterioration of the ease of control usually become higherwhen the current flowing through the armature winding lies in a lowcurrent region than when the current lies in a high current range.

In this regard, the above structure is designed to set the switchingfrequency for the switches in the low current range in which a lowerelectrical current flows through the armature winding to be higher thanthat in the high current range which is higher in electrical currentthan the low current range and in which a higher electrical currentflows through the armature winding, thereby minimizing the deteriorationof the ease of control of electrical current in the low current range.

When the electrical current flowing through the armature winding lies inthe high current range, the switching frequency is selected to be higherthan that in the low current range, thereby reducing a switching loss ofa power converter in the high current range.

The nineteenth means is a rotating electrical machine which comprises:(a) a magnetic field-producing unit equipped with a magnet unitincluding a plurality of magnetic poles whose magnetic polarities arearranged alternately in a circumferential direction; and (b) an armaturewhich includes a multi-phase armature winding. One of the magneticfield-producing unit and the armature is engineered as a rotor whoserotating shaft is retained by bearings to be rotatable. The rotatingshaft is retained by the plurality of bearings to be rotatable. Each ofthe bearings is offset from an axial center of one of the magneticfield-producing unit and the armature which works as the rotor to one ofopposed ends thereof in the axial direction.

The rotating electrical machine in the nineteenth means may be designedto have all possible combinations of the structures in the eighth totenth means.

The twentieth means is a rotating electrical machine which comprises:(a) a magnetic field-producing unit equipped with a magnet unitincluding a plurality of magnetic poles whose magnetic polarities arearranged alternately in a circumferential direction; and (b) an armaturewhich includes a multi-phase armature winding. One of the magneticfield-producing unit and the armature is engineered as a rotor whoserotating shaft is retained by bearings to be rotatable. The armatureincludes a ring-shaped base member which is disposed integrally with thearmature winding and secured to an armature holder. The armature windingis covered with a molding material along with the base member.

The rotating electrical machine in the twentieth means may be designedto have any possible combinations of the structures in the twelfth toseventeenth means.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described object, another object, features, or beneficialadvantages in this disclosure will be apparent from the appendeddrawings or the following detailed discussion.

In the drawings:

FIG. 1 is a perspective longitudinal sectional view of a rotatingelectrical machine.

FIG. 2 is a longitudinal sectional view of a rotating electricalmachine.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2.

FIG. 4 is a partial enlarged sectional view of FIG. 3.

FIG. 5 is an exploded view of a rotating electrical machine.

FIG. 6 is an exploded view of an inverter unit.

FIG. 7 is a torque diagrammatic view which demonstrates a relationshipbetween ampere-turns and a torque density in a stator winding.

FIG. 8 is a transverse sectional view of a rotor and a stator.

FIG. 9 is an enlarged view of part of FIG. 8.

FIG. 10 is a transverse sectional view of a stator.

FIG. 11 is a longitudinal sectional view of a stator.

FIG. 12 is a perspective view of a stator winding.

FIG. 13 is a perspective view of a conductor.

FIG. 14 is a schematic view illustrating a structure of wire.

FIGS. 15(a) and 15(b) are views showing the layout of conductors at then^(th) layer position.

FIG. 16 is a side view showing conductors at the n^(th) layer positionand the (n+1)^(th) layer position.

FIG. 17 is a view representing a relation between an electrical angleand a magnetic flux density in magnets of an embodiment.

FIG. 18 is a view which represents a relation between an electricalangle and a magnetic flux density in a comparative example of magnetarrangement.

FIG. 19 is an electrical circuit diagram of a control system for arotating electrical machine.

FIG. 20 is a functional block diagram which shows a current feedbackcontrol operation of a control device.

FIG. 21 is a functional block diagram which shows a torque feedbackcontrol operation of a control device.

FIG. 22 is a transverse sectional view of a rotor and a stator in thesecond embodiment.

FIG. 23 is a partial enlarged view of FIG. 22.

FIGS. 24(a) and 24(b) are views demonstrating flows of magnetic flux ina magnet unit.

FIG. 25 is a sectional view of a stator in the first modification.

FIG. 26 is a sectional view of a stator in the first modification.

FIG. 27 is a sectional view of a stator in the second modification.

FIG. 28 is a sectional view of a stator in the third modification.

FIG. 29 is a sectional view of a stator in the fourth modification.

FIG. 30 is a sectional view of a stator in the sixth modification.

FIG. 31 is a sectional view of a stator in the seventh modification.

FIG. 32 is a sectional view of a stator in the eighth modification.

FIG. 33 is a sectional view of a stator in the ninth modification.

FIG. 34 is a sectional view of a stator in the tenth modification.

FIG. 35 is a sectional view of a stator in the eleventh modification.

FIGS. 36(a) and 36(b) are schematic views which show a skew structure ofa rotor in the twelfth modification.

FIGS. 37(a) and 37(b) are schematic views which show a skew structure ofa stator in the thirteenth modification.

FIG. 38 is a transverse sectional view which illustrates a rotor and astator in the fifteenth modification.

FIG. 39 is a functional block diagram which illustrates a portion ofoperations of an operation signal generator in the sixteenthmodification.

FIG. 40 is a flowchart representing a sequence of steps to execute acarrier frequency altering operation.

FIGS. 41(a), 41(b), and 41(c) are views which illustrate connections ofconductors constituting a conductor group in the seventeenthmodification.

FIG. 42 is a view which illustrates a stack of four pairs of conductorsin the seventeenth modification.

FIG. 43 is a longitudinal sectional view which shows a structure of arotor in the eighteenth modification.

FIG. 44 is a transverse sectional view of an inner rotor type rotor anda stator in the nineteenth modification.

FIG. 45 is a partial enlarged view of FIG. 44.

FIG. 46 is a longitudinal sectional view of an inner rotor type rotatingelectrical machine.

FIG. 47 is a longitudinal sectional view which schematically illustratesa structure of an inner rotor type rotating electrical machine.

FIGS. 48(a) and 48(b) are sectional views which illustrate a regionclose to a rotating shaft in the twentieth modification.

FIG. 49 is a view which illustrates a structure of an inner rotor typerotating electrical machine in the twenty-first modification.

FIG. 50 is a view which illustrates a structure of an inner rotor typerotating electrical machine in the twenty-first modification.

FIG. 51 is a view which illustrates a structure of a revolving armaturetype of rotating electrical machine in the twenty-second modification.

FIG. 52 is a sectional view which illustrates a structure of a conductorin the twenty-fourth modification.

FIG. 53 is a view which illustrates a relation among reluctance torque,magnet torque, and distance DM.

FIG. 54 is a view which illustrates teeth.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The embodiments will be described below with reference to the drawings.Parts of the embodiments functionally or structurally corresponding toeach other or associated with each other will be denoted by the samereference numbers or by reference numbers which are different in thehundreds place from each other. The corresponding or associated partsmay refer to the explanation in the other embodiments.

The rotating electrical machine in the embodiments is configured to beused, for example, as a power source for vehicles. The rotatingelectrical machine may, however, be used widely for industrial,automotive, domestic, office automation, or game applications. In thefollowing embodiments, the same or equivalent parts will be denoted bythe same reference numbers in the drawings, and explanation thereof indetail will be omitted.

First Embodiment

The rotating electrical machine 10 in this embodiment is a synchronouspolyphase ac motor having an outer rotor structure (i.e., an outerrotating structure). The outline of the rotating electrical machine 10is illustrated in FIGS. 1 to 5. FIG. 1 is a perspective longitudinalsectional view of the rotating electrical machine 10. FIG. 2 is alongitudinal sectional view along the rotating shaft 11 of the rotatingelectrical machine 10. FIG. 3 is a traverse sectional view (i.e.,sectional view taken along the line III-III in FIG. 2) of the rotatingelectrical machine 10 perpendicular to the rotating shaft 11. FIG. 4 isa partially enlarged sectional view of FIG. 3. FIG. 5 is an explodedview of the rotating electrical machine 10. FIG. 3 omits hatchingshowing a section except the rotating shaft 11 for the sake ofsimplicity of the drawings. In the following discussion, a lengthwisedirection of the rotating shaft 11 will also be referred to as an axialdirection. A radial direction from the center of the rotating shaft 11will be simply referred to as a radial direction. A direction along acircumference of the rotating shaft 11 about the center thereof will besimply referred to as a circumferential direction.

The rotating electrical machine 10 includes the bearing unit 20, thehousing 30, the rotor 40, the stator 50, and the inverter unit 60. Thesemembers are arranged coaxially with each other together with therotating shaft 11 and assembled in a given sequence to complete therotating electrical machine 10.

The rotating electrical machine 10 in this embodiment is equipped withthe rotor 40 working as a magnetic field-producing unit or a fieldsystem and the stator 50 working as an armature and engineered as arevolving-field type rotating electrical machine.

The bearing unit 20 includes two bearings 21 and 22 arranged away fromeach other in the axial direction and the retainer 23 which retains thebearings 21 and 22. The bearings 21 and 22 are implemented by, forexample, radial ball bearings each of which includes the outer race 25,the inner race 26, and a plurality of balls 27 disposed between theouter race 25 and the inner race 26. The retainer 23 is of a cylindricalshape. The bearings 21 and 22 are disposed radially inside the retainer23. The rotating shaft 11 and the rotor 40 are retained radially insidethe bearings 21 and 22 to be rotatable. The bearings 21 and 22 are usedas a set of bearings to rotatably retain the rotating shaft 11.

Each of the bearings 21 and 22 holds the balls 27 using a retainer, notshown, to keep a pitch between the balls 27 constant. Each of thebearings 21 and 22 is equipped with seals on axially upper and lowerends of the retainer and also has non-conductive grease (e.g.,non-conductive urease grease) installed inside the seals. The positionof the inner race 26 is mechanically secured by a spacer to exertconstant inner precompression on the inner race 26 in the form of avertical convexity.

The housing 30 includes the cylindrical peripheral wall 31. Theperipheral wall 31 has a first end and a second end opposed to eachother in an axial direction thereof. The peripheral wall 31 has the endsurface 32 on the first end and the opening 33 in the second end. Theopening 33 occupies the entire area of the second end. The end surface32 has formed in the center thereof the circular hole 34. The bearingunit 20 is inserted into the hole 34 and fixed using a fastener, such asa screw or a rivet. The hollow cylindrical rotor 40 and the hollowcylindrical stator 50 are disposed in an inner space defined by theperipheral wall 31 and the end surface 32 within the housing 30. In thisembodiment, the rotating electrical machine 10 is of an outer rotortype, so that the stator 50 is arranged radially inside the cylindricalrotor 40 within the housing 30. The rotor 40 is retained in a cantileverform by a portion of the rotating shaft 11 close to the end surface 32in the axial direction.

The rotor 40 includes the hollow cylindrical magnetic holder 41 and theannular magnet unit 42 disposed radially inside the magnet holder 41.The magnet holder 41 is of substantially a cup-shape and works as amagnet holding member. The magnet holder 41 includes the cylinder 43,the attaching portion 44 which is of a cylindrical shape and smaller indiameter than the cylinder 43, and the intermediate portion 45connecting the cylinder 43 and the attaching portion 44 together. Thecylinder 43 has the magnet unit 42 secured to an inner peripheralsurface thereof.

The magnet holder 41 is made of cold rolled steel (SPCC), forging steel,or carbon fiber reinforced plastic (CFRP) which have a required degreeof mechanical strength.

The rotating shaft 11 passes through the through-hole 44 a of theattaching portion 44. The attaching portion 44 is secured to a portionof the rotating shaft 11 disposed inside the through-hole 44 a. In otherwords, the magnet holder 41 is secured to the rotating shaft 11 throughthe attaching portion 44. The attaching portion 44 may preferably bejoined to the rotating shaft 11 using concavities and convexities, suchas a spline joint or a key joint, welding, or crimping, so that therotor 40 rotates along with the rotating shaft 11.

The bearings 21 and 22 of the bearing unit 20 are secured radiallyoutside the attaching portion 44. The bearing unit 20 is, as describedabove, fixed on the end surface 32 of the housing 30, so that therotating shaft 11 and the rotor 40 are retained by the housing 30 to berotatable. The rotor 40 is, thus, rotatable within the housing 30.

The rotor 40 is equipped with the attaching portion 44 arranged only oneof ends thereof opposed to each other in the axial direction of therotor 40. This cantilevers the rotor 40 on the rotating shaft 11. Theattaching portion 44 of the rotor 40 is rotatably retained at two pointsof supports using the bearings 21 and 22 of the bearing unit 20 whichare located away from each other in the axial direction. In other words,the rotor 40 is held to be rotatable using the two bearings 21 and 22which are separate at a distance away from each other in the axialdirection on one of the axially opposed ends of the magnet holder 41.This ensures the stability in rotation of the rotor 40 even though therotor 40 is cantilevered on the rotating shaft 11. The rotor 40 isretained by the bearings 21 and 22 at locations which are away from thecenter intermediate between the axially opposed ends of the rotor 40 inthe axial direction thereof.

The bearing 22 of the bearing unit 20 which is located closer to thecenter of the rotor 40 (a lower one of the bearings 21 and 22 in thedrawings) is different in dimension of a gap between each of the outerrace 25 and the inner race and the balls 27 from the bearing 21 which islocated farther away from the center of the rotor 40 (i.e., an upper oneof the bearings 21 and 22). For instance, the bearing 22 closer to thecenter of the rotor 40 is greater in the dimension of the gap from thebearing 21. This minimizes adverse effects on the bearing unit 20 whicharise from deflection of the rotor 40 or mechanical vibration of therotor 40 due to imbalance resulting from parts tolerance at a locationclose to the center of the rotor 40. Specifically, the bearing 22 closerto the center of the rotor 40 is engineered to have dimensions of thegaps or plays increased using precompression, thereby absorbing thevibration generating in the cantilever structure. The precompression maybe provided by either fixed position preload or constant pressurepreload. In the case of the fixed position preload, the outer race 25 ofeach of the bearings 21 and 22 is joined to the retainer 23 usingpress-fitting or welding. The inner race 26 of each of the bearings 21and 22 is joined to the rotating shaft 11 by press-fitting or welding.The precompression may be created by placing the outer race 25 of thebearing 21 away from the inner race 26 of the bearing 21 in the axialdirection or alternatively placing the outer race 25 of the bearing 22away from the inner race 26 of the bearing 22 in the axial direction.

In the case of the constant pressure preload, a preload spring, such asa wave washer 24, is arranged between the bearing 22 and the bearing 21to create the preload directed from a region between the bearing 22 andthe bearing 21 toward the outer race 25 of the bearing 22 in the axialdirection. In this case, the inner race 26 of each of the bearing 21 andthe bearing 22 is joined to the rotating shaft 11 using press fitting orbonding. The outer race 25 of the bearing 21 or the bearing 22 isarranged away from the outer race 25 through a given clearance. Thisstructure exerts pressure, as produced by the preload spring, on theouter race 25 of the bearing 22 to urge the outer race 25 away from thebearing 21. The pressure is then transmitted through the rotating shaft11 to urge the inner race 26 of the bearing 21 toward the bearing 22,thereby bringing the outer race 25 of each of the bearings 21 and 22away from the inner race 26 thereof in the axial direction to exert thepreload on the bearings 21 and 22 in the same way as the fixed positionpreload.

The constant pressure preload does not necessarily need to exert thespring pressure, as illustrated in FIG. 2, on the outer race 25 of thebearing 22, but may alternatively be created by exerting the springpressure on the outer race 25 of the bearing 21. The exertion of thepreload on the bearings 21 and 22 may alternatively be achieved byplacing the inner race 26 of one of the bearings 21 and 22 away from therotating shaft 11 through a given clearance therebetween and joining theouter race 25 of each of the bearings 21 and 22 to the retainer 23 usingpress-fitting or bonding.

Further, in the case where the pressure is created to bring the innerrace 26 of the bearing 21 away from the bearing 22, such pressure ispreferably additionally exerted on the inner race 26 of the bearing 22away from the bearing 21. Conversely, in the case where the pressure iscreated to bring the inner race 26 of the bearing 21 close to thebearing 22, such pressure is preferably additionally exerted on theinner race 26 of the bearing 22 to bring it close to the bearing 21.

In a case where the rotating electrical machine 10 is used as a powersource for a vehicle, there is a risk that mechanical vibration having acomponent oriented in a direction in which the preload is created may beexerted on the preload generating structure or that a direction in whichthe force of gravity acts on an object to which the preload is appliedmay be changed. In order to alleviate such a problem, the fixed positionpreload is preferably used in the case where the rotating electricalmachine 10 is mounted in the vehicle.

The intermediate portion 45 includes the annular inner shoulder 49 a andthe annular outer shoulder 49 b. The outer shoulder 49 b is arrangedoutside the inner shoulder 49 a in the radial direction of theintermediate portion 45. The inner shoulder 49 a and the outer shoulder49 b are separate from each other in the axial direction of theintermediate portion 45. This layout results in a partial overlapbetween the cylinder 43 and the attaching portion 44 in the radialdirection of the intermediate portion 45. In other words, the cylinder43 protrudes outside a base end portion (i.e., a lower portion, asviewed in the drawing) of the attaching portion 44 in the axialdirection. The structure in this embodiment enables the rotor 40 to beretained by the rotating shaft 11 at a location closer to the center ofgravity of the rotor 40 than a case where the intermediate portion 45 isshaped to be flat without any shoulder, thereby ensuring the stabilityin operation of the rotor 40.

In the above described structure of the intermediate portion 45, therotor 40 has the annular bearing housing recess 46 which is formed in aninner portion of the intermediate portion 45 and radially surrounds theattaching portion 44. The bearing housing recess 46 has a portion of thebearing unit 20 disposed therein. The rotor 40 also has the coil housingrecess 47 which is formed in an outer portion of the intermediateportion 45 and radially surrounds the bearing housing recess 46. Thecoil housing recess 47 has disposed therein the coil end 54 of thestator winding 51 of the stator 50, which will be described later indetail. The housing recesses 46 and 47 are arranged adjacent each otherin the axial direction. In other words, a portion of the bearing unit 20is laid to overlap the coil end 54 of the stator winding 51 in the axialdirection. This enables the rotating electrical machine 10 to have alength decreased in the axial direction.

The intermediate portion 45 extends or overhangs outward from therotating shaft 11 in the radial direction. The intermediate portion 45is equipped with a contact avoider which extends in the axial directionand avoids a physical contact with the coil end 54 of the stator winding51 of the stator 50. The intermediate portion 45 will also be referredto as an overhang.

The coil end 54 may be bent radially inwardly or outwardly to have adecreased axial dimension, thereby enabling the axial length of thestator 50 to be decreased. A direction in which the coil end 54 is bentis preferably determined depending upon installation thereof in rotor40. In the case where the stator 50 is installed radially inside therotor 40, a portion of the coil end 54 which is inserted into the rotor40 is preferably bent radially inwardly. A coil end opposite the coilend 54 may be bent either inwardly or outwardly, but is preferably bentto an outward side where there is an enough space in terms of theproduction thereof.

The magnet unit 42 working as a magnetic portion is made up of aplurality of permanent magnets which are disposed radially inside thecylinder 43 to have different magnetic poles arranged alternately in acircumferential direction thereof. The magnet unit 42, thus, has aplurality of magnetic poles arranged in the circumferential direction.The magnet unit 42 will also be described later in detail.

The stator 50 is arranged radially inside the rotor 40. The stator 50includes the stator winding 51 wound in a substantially cylindrical(annular) form and the stator core 52 used as a base member arrangedradially inside the stator winding 51. The stator winding 51 is arrangedto face the annular magnet unit 42 through a given air gap therebetween.The stator winding 51 includes a plurality of phase windings each ofwhich is made of a plurality of conductors which are arranged at a givenpitch away from each other in the circumferential direction and joinedtogether. In this embodiment, two three-phase windings: one including aU-phase winding, a V-phase winding, and a W-phase winging and the otherincluding an X-phase winding, a Y-phase winding, and a Z-phase windingare used to complete the stator winding 51 as a six-phase winding.

The stator core 52 is formed by an annular stack of magnetic steelplates made of soft magnetic material and mounted radially inside thestator winding 51. The magnetic steel plates are, for example, siliconnitride steel plates made by adding a small percent (e.g., 3%) ofsilicon nitride to iron. The stator winding 51 corresponds to anarmature winding. The stator core 52 corresponds to an armature core.

The stator winding 51 overlaps the stator core 52 in the radialdirection and includes the coil side portion 53 disposed radiallyoutside the stator core 52 and the coil ends 54 and 55 overhanging atends of the stator core 52 in the axial direction. The coil side portion53 faces the stator core 52 and the magnet unit 42 of the rotor 40 inthe radial direction. The stator 50 is arranged inside the rotor 40. Thecoil end 54 that is one (i.e., an upper one, as viewed in the drawings)of the axially opposed coil ends 54 and 55 and arranged close to thebearing unit 20 is disposed in the coil housing recess 47 defined by themagnet holder 41 of the rotor 40. The stator 50 will also be describedlater in detail.

The inverter unit 60 includes the unit base 61 secured to the housing 30using fasteners, such as bolts, and a plurality of electrical components62 mounted on the unit base 61. The unit base 61 is made from, forexample, carbon fiber reinforced plastic (CFRP). The unit base 61includes the end plate 63 secured to an edge of the opening 33 of thehousing 30 and the casing 64 which is formed integrally with the endplate 63 and extends in the axial direction. The end plate 63 has thecircular opening 65 formed in the center thereof. The casing 64 extendsupward from a peripheral edge of the opening 65.

The stator 50 is arranged on an outer peripheral surface of the casing64. Specifically, an outer diameter of the casing 64 is selected to beidentical with or slightly smaller than an inner diameter of the statorcore 52. The stator core 52 is attached to the outer side of the casing64 to complete a unit made up of the stator 50 and the unit base 61. Theunit base 61 is secured to the housing 30, so that the stator 50 isunified with the housing 50 in a condition where the stator core 52 isinstalled on the casing 64.

The stator core 52 may be bonded, shrink-fit, or press-fit on the unitbase 61, thereby eliminating positional shift of the stator core 52relative to the unit base 61 both in the circumferential direction andin the axial direction.

The casing 64 has a radially inner storage space in which the electricalcomponents 62 are disposed. The electrical components 62 are arranged tosurround the rotating shaft 11 within the storage space. The casing 64functions as a storage space forming portion. The electrical components62 include the semiconductor modules 66, the control board 67, and thecapacitor module 68 which constitute an inverter circuit.

The unit base 61 serves as a stator holder (i.e., an armature holder)which is arranged radially inside the stator 50 and retains the stator50. The housing 30 and the unit base 61 define a motor housing for therotating electrical machine 10. In the motor housing, the retainer 23 issecured to a first end of the housing 30 which is opposed to a secondend of the housing 30 through the rotor 40 in the axial direction. Thesecond end of the housing 30 and the unit base 61 are joined together.For instance, in an electric-powered vehicle, such as an electricautomobile, the motor housing is attached to a side of the vehicle toinstall the rotating electrical machine 10 in the vehicle.

The inverter unit 60 will be also be described using FIG. 6 that is anexploded view in addition to FIGS. 1 to 5.

The casing 64 of the unit base 61 includes the cylinder 71 and the endsurface 72 that is one of ends of the cylinder 71 which are opposed toeach other in the axial direction of the cylinder 71 (i.e., the end ofthe casing 64 close to the bearing unit 20). The end of the cylinder 71opposed to the end surface 72 in the axial direction is shaped to fullyopen to the opening 65 of the end plate 63. The end surface 72 hasformed in the center thereof the circular hole 73 through which therotating shaft 11 is insertable. The hole 73 has fitted therein thesealing member 171 which hermetically seals an air gap between the hole73 and the outer periphery of the rotating shaft 11. The sealing member171 is preferably implemented by, for example, a resinous slidable seal.

The cylinder 71 of the casing 64 serves as a partition which isolatesthe rotor 40 and the stator 50 arranged radially outside the cylinder 71from the electrical components 62 arranged radially inside the cylinder71. The rotor 40, the stator 50, and the electrical components 62 arearranged radially inside and outside the cylinder 71.

The electrical components 62 are electrical devices making up theinverter circuit equipped with a motor function and a generatorfunction. The motor function is to deliver electrical current to thephase windings of the stator winding 51 in a given sequence to turn therotor 40. The generator function is to receive a three-phase ac currentflowing through the stator winding 51 in response to the rotation of therotating shaft 11 and generate and output electrical power. Theelectrical components 62 may be engineered to perform either one of themotor function and the generator function. In a case where the rotatingelectrical machine 10 is used as a power source for a vehicle, thegenerator function serves as a regenerative function to output aregenerated electrical power.

Specifically, the electrical components 62, as demonstrated in FIG. 4,include the hollow cylindrical capacitor module 68 arranged around therotating shaft 11 and the semiconductor modules 66 mounted on thecapacitor module 68. The capacitor module 68 has a plurality ofsmoothing capacitors 68 a connected in parallel to each other.Specifically, each of the capacitors 68 a is implemented by astacked-film capacitor which is made of a plurality of film capacitorsstacked in a trapezoidal shape in cross section. The capacitor module 68is made of the twelve capacitors 68 a arranged in an annular shape.

The capacitors 68 a may be produced by preparing a long film which has agiven width and is made of a stack of films and cutting the long filminto isosceles trapezoids each of which has a height identical with thewidth of the long film and whose short bases and long bases arealternately arranged. Electrodes are attached to the thus producedcapacitor devices to complete the capacitors 68 a.

The semiconductor module 66 includes, for example, a semiconductorswitch, such as a MOSFET or an IGBT and is of substantially a planarshape. In this embodiment, the rotating electrical machine 10 is, asdescribed above, equipped with two sets of three-phase windings and hasthe inverter circuits, one for each set of the three-phase windings. Theelectrical components 62, therefore, include a total of twelvesemiconductor modules 66 which are arranged in an annular form to makeup the semiconductor module group 66A.

The semiconductor modules 66 are interposed between the cylinder 71 ofthe casing 64 and the capacitor module 68. The semiconductor modulegroup 66A has an outer peripheral surface placed in contact with aninner peripheral surface of the cylinder 71. The semiconductor modulegroup 66A also has an inner peripheral surface placed in contact with anouter peripheral surface of the capacitor module 68. This causes heat,as generated in the semiconductor modules 66, to be transferred to theend plate 63 through the casing 64, so that it is dissipated from theend plate 63.

The semiconductor module group 66A preferably has the spacers 69disposed radially outside the outer peripheral surface thereof, i.e.,between the semiconductor modules 66 and the cylinder 71. A combinationof the capacitor modules 68 is so arranged as to have a regulardodecagonal section extending perpendicular to the axial directionthereof, while the inner periphery of the cylinder 71 has a circulartransverse section.

The spacers 69 are, therefore, each shaped to have a flat innerperipheral surface and a curved outer peripheral surface. The spacers 69may alternatively be formed integrally with each other in an annularshape and disposed radially outside the semiconductor module group 66A.The spacers 69 are highly thermally conductive and made of, for example,metal, such as aluminum or heat dissipating gel sheet. The innerperiphery of the cylinder 71 may alternatively be shaped to have adodecagonal transverse section like the capacitor modules 68. In thiscase, the spacers 69 are each preferably shaped to have a flat innerperipheral surface and a flat outer peripheral surface.

In this embodiment, the cylinder 71 of the casing 64 has formed thereinthe coolant path 74 through which coolant flows. The heat generated inthe semiconductor modules 66 is also released to the coolant flowing inthe coolant path 74. In other words, the casing 64 is equipped with acooling mechanism. The coolant path 74 is, as clearly illustrated inFIGS. 3 and 4, formed in an annular shape and surrounds the electricalcomponents 62 (i.e., the semiconductor modules 66 and the capacitormodule 68). The semiconductor modules 66 are arranged along the innerperipheral surface of the cylinder 71. The coolant path 74 is laid tooverlap the semiconductor modules 66 in the radial direction.

The stator 50 is arranged outside the cylinder 71. The electricalcomponents 62 are arranged inside the cylinder 71. This layout causesthe heat to be transferred from the stator 50 to the outer side of thecylinder 71 and also transferred from the electrical components 62(e.g., the semiconductor modules 66) to the inner side of the cylinder71. It is possible to simultaneously cool the stator 50 and thesemiconductor modules 66, thereby facilitating dissipation of thermalenergy generated by heat-generating members of the rotating electricalmachine 10.

Further, at least one of the semiconductor modules 66 which constitutepart or all of the inverter circuits serving to energize the statorwinding 51 to drive the rotating electrical machine is arranged in aregion surrounded by the stator core 52 disposed radially outside thecylinder 71 of the casing 64. Preferably, one of the semiconductormodules 66 may be arranged fully inside the region surrounded by thestator core 52. More preferably, all the semiconductor modules 66 may bearranged fully in the region surrounded by the stator core 52.

At least a portion of the semiconductor modules 66 is arranged in aregion surrounded by the coolant path 74. Preferably, all thesemiconductor modules 66 may be arranged in a region surrounded by theyoke 141.

The electrical components 62 include the insulating sheet 75 disposed onone of axially opposed end surfaces of the capacitor module 68 and thewiring module 76 disposed on the other end surface of the capacitormodule 68. The capacitor module 68 has two axially-opposed end surfaces:a first end surface and a second end surface. The first end surface ofthe capacitor module 68 closer to the bearing unit 20 faces the endsurface 72 of the casing 64 and is laid on the end surface 72 throughthe insulating sheet 75. The second end surface of the capacitor module68 closer to the opening 65 has the wiring module 76 mounted thereon.

The wiring module 76 includes the resin-made circular plate-shaped body76 a and a plurality of bus bars 76 b and 76 c embedded in the body 76a. The bus bars 76 b and 76 c electrically connect the semiconductormodules 66 and the capacitor module 68 together. Specifically, thesemiconductor modules 66 are equipped with the connecting pins 66 aextending from axial ends thereof. The connecting pins 66 a connect withthe bus bars 76 b radially outside the body 76 a. The bus bars 76 cextend away from the capacitor module 68 radially outside the body 76 aand have top ends connecting with the wiring members 79 (see FIG. 2).

The capacitor module 68, as described above, has the insulating sheet 75mounted on the first end surface thereof. The capacitor module 68 alsohas the wiring module 76 mounted on the second end surface thereof. Thecapacitor module 68, therefore, has two heat dissipating paths whichextend from the first and second end surfaces of the capacitor module 68to the end surface 72 and the cylinder 71. Specifically, the heatdissipating path is defined which extends from the first end surface tothe end surface 72. The heat dissipating path is defined which extendsfrom the second end surface to the cylinder 71. This enables the heat tobe released from the end surfaces of the capacitor module 68 other thanthe outer peripheral surface on which the semiconductor modules 66 arearranged. In other words, it is possible to dissipate the heat not onlyin the radial direction, but also in the axial direction.

The capacitor module 68 is of a hollow cylindrical shape and has therotating shaft 11 arranged therewithin at a given interval away from theinner periphery of the capacitor module 68, so that heat generated bythe capacitor module 68 will be dissipated from the hollow cylindricalspace. The rotation of the rotating shaft 11 usually produces a flow ofair, thereby enhancing cooling effects.

The wiring module 76 has the disc-shaped control board 67 attachedthereto. The control board 67 includes a printed circuit board (PCB) onwhich given wiring patterns are formed and also has ICs and the controldevice 77 mounted thereon. The control device 77 serves as a controllerand is made of a microcomputer. The control board 67 is secured to thewiring module 76 using fasteners, such as screws. The control board 67has formed in the center thereof the hole 67 a through which therotating shaft 11 passes.

The wiring module 76 has a first surface and a second surface opposed toeach other in the axial direction, that is, a thickness-wise directionof the wiring module 76. The first surface faces the capacitor module68. The wiring module 76 has the control board 67 mounted on the secondsurface thereof. The bus bars 76 c of the wiring module 76 extend fromone of surfaces of the control board 67 to the other. The control board67 may have cut-outs for avoiding physical interference with the busbars 76 c. For instance, the control board 67 may have the cut-outsformed in portions of the circular outer edge thereof.

The electrical components 62 are, as described already, arranged insidethe space surrounded by the casing 64. The housing 30, the rotor 40, andthe stator 50 are disposed outside the space in the form of layers. Thisstructure serves to shield against electromagnetic noise generated inthe inverter circuits. Specifically, the inverter circuit works tocontrol switching operations of the semiconductor modules 66 in a PWMcontrol mode using a given carrier frequency. The switching operationsusually generate electromagnetic noise against which the housing 30, therotor 40, and the stator 50 which are arranged outside the electricalcomponents 62 shield.

Further, at least a portion of the semiconductor modules 66 is arrangedinside the region surrounded by the stator core 52 located radiallyoutside the cylinder 71 of the casing 64, thereby minimizing adverseeffects of magnetic flux generated by the semiconductor modules 66 onthe stator winding 51 as compared with a case where the semiconductormodules 66 and the stator winding 51 are arranged without the statorcore 52 interposed therebetween. The magnetic flux created by the statorwinding 51 also hardly affects the semiconductor modules 66. It is moreeffective that the whole of the semiconductor modules 66 are located inthe region surrounded by the stator core 52 disposed radially outsidethe cylinder 71 of the casing 64. When at least a portion of thesemiconductor modules 66 is surrounded by the coolant path 74, it offersa beneficial advantage that the heat produced by the stator winding 51or the magnet unit 42 is prevented from reaching the semiconductormodules 66.

The cylinder 71 has the through-holes 78 which are formed near the endplate 63 and through which the wiring members 79 (see FIG. 2) pass toelectrically connect the stator 50 disposed outside the cylinder 71 andthe electrical components 62 arranged inside the cylinder 71. The wiringmembers 79, as illustrated in FIG. 2, connect with ends of the statorwinding 51 and the bus bars 76 c of the wiring module 76 using crimpingor welding techniques. The wiring members 79 are implemented by, forexample, bus bars whose joining surfaces are preferably flattened. Asingle through-hole 78 or a plurality of through-holes 78 are preferablyprovided. This embodiment has two through-holes 78. The use of the twothrough-holes 78 facilitates the ease with which terminals extendingfrom the two sets of the three-phase windings are connected by thewiring members 79, and is suitable for achieving multi-phase wireconnections.

The rotor 40 and the stator 50 are, as described already in FIG. 4,arranged within the housing 30 in this order in a radially inwarddirection. The inverter unit 60 is arranged radially inside the stator50. If a radius of the inner periphery of the housing 30 is defined asd, the rotor 40 and the stator 50 are located radially outside adistance of d×0.705 away from the center of rotation of the rotor 40. Ifa region located radially inside the inner periphery of the stator 50(i.e., the inner circumferential surface of the stator core 52) isdefined as a first region X1, and a region radially extending from theinner periphery of the stator 50 to the housing 30 is defined as asecond region X2, an area of a transverse section of the first region X1is set greater than that of the second region X2. As viewed in a regionwhere the magnet unit 42 of the rotor 40 overlaps the stator winding 51,the volume of the first region X1 is larger than that of the secondregion X2.

The rotor 40 and the stator 50 are fabricated as a magnetic circuitcomponent assembly. In the housing 30, the first region X1 which islocated radially inside the inner peripheral surface of the magneticcircuit component assembly is larger in volume than the region X2 whichlies between the inner peripheral surface of the magnetic circuitcomponent assembly and the housing 30 in the radial direction.

Next, the structures of the rotor 40 and the stator 50 will be describedbelow in more detail.

Typical rotating electrical machines are known which are equipped with astator with an annular stator core which is made of a stack of steelplates and has a stator winding wound in a plurality of slots arrangedin a circumferential direction of the stator core. Specifically, thestator core has teeth extending in a radial direction thereof at a giveninterval away from a yoke. Each slot is formed between the two radiallyadjacent teeth. In each slot, a plurality of conductors are arranged inthe radial direction in the form of layers to form the stator winding.

However, the above described stator structure has a risk that when thestator winding is energized, an increase in magnetomotive force in thestator winding may result in magnetic saturation in the teeth of thestator core, thereby restricting torque density in the rotatingelectrical machine. In other words, rotational flux, as created by theenergization of the stator winding of the stator core, is thought of asconcentrating on the teeth, which has a risk of causing magneticsaturation.

Generally, IPM (Interior Permanent Magnet) rotors are known which have astructure in which permanent magnets are arranged on a d-axis of a d-qaxis coordinate system, and a rotor core is placed on a q-axis of thed-q axis coordinate system. Excitation of a stator winding near thed-axis will cause an excited magnetic flux to flow from a stator to arotor according to Fleming's rules. This causes magnetic saturation tooccur widely in the rotor core on the q-axis.

FIG. 7 is a torque diagrammatic view which demonstrates a relationshipbetween an ampere-turn (AT) representing a magnetomotive force createdby the stator winding and a torque density (Nm/L). A broken lineindicates characteristics of a typical IPM rotor-rotating electricalmachine. FIG. 7 shows that in the typical rotating electrical machine,an increase in magnetomotive force in the stator will cause magneticsaturation to occur at two places: the tooth between the slots and theq-axis rotor (i.e., the rotor core on the q-axis), thereby restrictingan increase in torque. In this way, a design value of the ampere-turn isrestricted at A1 in the typical rotating electrical machine.

In order to alleviate the above problem in this embodiment, the rotatingelectrical machine 10 is designed to have an additional structure, aswill be described below, in order to eliminate the restriction arisingfrom the magnetic saturation. Specifically, as a first measure, thestator 50 is designed to have a slot-less structure for eliminating themagnetic saturation occurring in the teeth of the stator core of thestator and also to use an SPM (Surface Permanent Magnet) rotor foreliminating the magnetic saturation occurring in a q-axis core of theIPM rotor. The first measure serves to eliminate the above described twoplaces where the magnetic saturation occurs, but however, may result ina decrease in torque in a low-current region (see an alternate long andshort dash line in FIG. 7). In order to alleviate this problem, as asecond measure, a polar anisotropy structure is employed to increase amagnetic path of magnets in the magnet unit 42 of the rotor 40 toenhance a magnetic force in order to increase a magnetic flux in the SPMrotor to minimize the torque decrease.

Additionally, as a third measure, a flattened conductor structure isemployed to decrease a thickness of conductors of the coil side portion53 of the stator winding 51 in the radial direction of the stator 50 forcompensating for the torque decrease. The above magnetic force-enhancedpolar anisotropy structure is thought of as resulting in a flow of largeeddy current in the stator winding 51 facing the magnet unit 42. Thethird measure is, however, to employ the flattened conductor structurein which the conductors have a decreased thickness in the radialdirection, thereby minimizing the generation of the eddy current in thestator winding 51 in the radial direction. In this way, the above firstto third structures are, as indicated by a solid line in FIG. 7,expected to greatly improve the torque characteristics usinghigh-magnetic force magnets and also alleviate a risk of generation of alarge eddy current resulting from the use of the high-magnetic forcemagnets.

Additionally, as a fourth measure, a magnet unit is employed which has apolar anisotropic structure to create a magnetic density distributionapproximating a sine wave. This increases a sine wave matchingpercentage using pulse control, as will be described later, to enhancethe torque and also results in a moderate change in magnetic flux,thereby minimizing an eddy-current loss (i.e., a copper loss caused byeddy current) as compared with radial magnets.

The sine wave matching percentage will be described below. The sine wavematching percentage may be derived by comparing a waveform, a cycle, anda peak value of a surface magnetic flux density distribution measured byactually moving a magnetic flux probe on a surface of a magnet withthose of a sine wave. The since wave matching percentage is given by apercentage of an amplitude of a primary waveform that is a waveform of afundamental wave in a rotating electrical machine to that of theactually measured waveform, that is, an amplitude of the sum of thefundamental wave and a harmonic component. An increase in the sine wavematching percentage will cause the waveform in the surface magnetic fluxdensity distribution to approach the waveform of the sine wave. When anelectrical current of a primary sine wave is delivered by an inverter toa rotating electrical machine equipped with magnets having an improvedsine wave matching percentage, it will cause a large degree of torque tobe produced, combined with the fact that the waveform in the surfacemagnetic flux density distribution of the magnet is close to thewaveform of a sine wave. The surface magnetic flux density distributionmay alternatively be derived using electromagnetic analysis according toMaxwell's equations.

As a fifth measure, the stator winding 51 is designed to have aconductor strand structure made of a bundle of wires. In the conductorstrand structure of the stator winding 51, the wires are connectedparallel to each other, thus enabling a high current or large amount ofcurrent to flow in the stator winding 51 and also minimizing an eddycurrent occurring in the conductors widened in the circumferentialdirection of the stator 50 more effectively than the third measure inwhich the conductors are flattened in the radial direction because eachof the wires has a decreased transverse sectional area. The use of thebundle of the wires will cancel an eddy current arising from magneticflux occurring according to Ampere's circuital law in response to themagnetomotive force produced by the conductors.

The use of the fourth and fifth measures minimizes the eddy-current lossresulting from the high magnetic force produced by the high-magneticforce magnets provided by the second measure and also enhance thetorque.

The slot-less structure of the stator 50, the flattened conductorstructure of the stator winding 51, and the polar anisotropy structureof the magnet unit 42 will be described below. The slot-less structureof the stator 50 and the flattened conductor structure of the statorwinding 51 will first be discussed. FIG. 8 is a transverse sectionalview illustrating the rotor 40 and the stator 50. FIG. 9 is a partiallyenlarged view illustrating the rotor 40 and the stator 50 in FIG. 8.FIG. 10 is a transverse sectional view of the stator 50 taken along theline X-X in FIG. 11. FIG. 11 is a longitudinal sectional view of thestator 50. FIG. 12 is a perspective view of the stator winding 51. FIGS.8 and 9 indicate directions of magnetization of magnets of the magnetunit 42 using arrows.

The stator core 52 is, as clearly illustrated in FIGS. 8 to 11, of acylindrical shape and made of a plurality of magnetic steel platesstacked in the axial direction of the stator core 52 to have a giventhickness in a radial direction of the stator core 52. The statorwinding 51 is mounted on the outer periphery of the stator core 52 whichfaces the rotor 40. The outer peripheral surface of the stator core 52facing the rotor 40 serves as a conductor mounting portion (i.e., aconductor area). The outer peripheral surface of the stator core 52 isshaped as a curved surface without any irregularities. A plurality ofconductor groups 81 are arranged on the outer peripheral surface of thestator core 52 at given intervals away from each other in thecircumferential direction of the stator core 52. The stator core 52functions as a back yoke that is a portion of a magnetic circuit workingto rotate the rotor 40. The stator 50 is designed to have a structure inwhich a tooth (i.e., a core) made of a soft magnetic material is notdisposed between a respective two of the conductor groups 81 arrangedadjacent each other in the circumferential direction (i.e., theslot-less structure). In this embodiment, a resin material of thesealing member 57 is disposed in the space or gap 56 between arespective adjacent two of the conductor groups 81. In other words, thestator 50 has a conductor-to-conductor member which is disposed betweenthe conductor groups 81 arranged adjacent each other in thecircumferential direction of the stator 50 and made of a non-magneticmaterial. The conductor-to-conductor members serve as the sealingmembers 57. Before the sealing members 57 are placed to seal the gaps56, the conductor groups 81 are arranged in the circumferentialdirection radially outside the stator core 52 at a given interval awayfrom each other through the gaps 56 that are conductor-to-conductorregions. This makes up the slot-less structure of the stator 50. Inother words, each of the conductor groups 81 is, as described later indetail, made of two conductors 82. An interval between a respective twoof the conductor groups 81 arranged adjacent each other in thecircumferential direction of the stator 50 is occupied only by anon-magnetic material. The non-magnetic material, as referred to herein,includes a non-magnetic gas, such as air, or a non-magnetic liquid. Inthe following discussion, the sealing members 57 will also be referredto as conductor-to-conductor members.

The structure, as referred to herein, in which the teeth arerespectively disposed between the conductor groups 81 arrayed in thecircumferential direction means that each of the teeth has a giventhickness in the radial direction and a given width in thecircumferential direction of the stator 50, so that a portion of themagnetic circuit, that is, a magnet magnetic path lies between theadjacent conductor groups 81. In contrast, the structure in which notooth lies between the adjacent conductor groups 81 means that there isno magnetic circuit between the adjacent conductor groups 81.

The stator winding (i.e., the armature winding) 51, as illustrated inFIG. 10, has a given thickness T2 (which will also be referred to belowas a first dimension) and a width W2 (which will also be referred tobelow as a second dimension). The thickness T2 is given by a minimumdistance between an outer side surface and an inner side surface of thestator winding 51 which are opposed to each other in the radialdirection of the stator 50. The width W2 is given by a dimension of aportion of the stator winding 51 which functions as one of multiplephases (i.e., the U-phase, the V-phase, the W-phase, the X-phase, theY-phase, and the Z-phase in this embodiment) of the stator winding 51 inthe circumferential direction. Specifically, in a case where the twoconductor groups 81 arranged adjacent each other in the circumferentialdirection in FIG. 10 serve as one of the three phases, for example, theU-phase winding, a distance between circumferentially outermost ends ofthe two circumferentially adjacent conductor groups 81 is the width W2.The thickness T2 is smaller than the width W2.

The thickness T2 is preferably set smaller than the sum of widths of thetwo conductor groups 81 within the width W2. If the stator winding 51(more specifically, the conductor 82) is designed to have a truecircular transverse section, an oval transverse section, or a polygonaltransverse section, the cross section of the conductor 82 taken in theradial direction of the stator 50 may be shaped to have a maximumdimension W12 in the radial direction of the stator 50 and a maximumdimension W11 in the circumferential direction of the stator 50.

The stator winding 51 is, as can be seen in FIGS. 10 and 11, sealed bythe sealing members 57 which are formed by a synthetic resin mold.Specifically, the stator winding 51 and the stator core 52 are put in amould together when the sealing members 57 are moulded by the resin. Theresin may be considered as a non-magnetic material or an equivalentthereof whose Bs (saturation magnetic flux density) is zero.

As a transverse section is viewed in FIG. 10, the sealing members 57 areprovided by placing synthetic resin in the gaps 56 between the conductorgroups 81. The sealing members 57 serve as insulators arranged betweenthe conductor groups 81. In other words, each of the sealing members 57functions as an insulator in one of the gaps 56. The sealing members 57occupy a region which is located radially outside the stator core 52,and includes all the conductor groups 81, in other words, which isdefined to have a dimension larger than that of each of the conductorgroups 81 in the radial direction.

As a longitudinal section is viewed in FIG. 11, the sealing members 57lie to occupy a region including the turns 84 of the stator winding 51.Radially inside the stator winding 51, the sealing members 57 lie in aregion including at least a portion of the axially opposed ends of thestator core 52. In this case, the stator winding 51 is fully sealed bythe resin except for the ends of each phase winding, i.e., terminalsjoined to the inverter circuits.

The structure in which the sealing members 57 are disposed in the regionincluding the ends of the stator core 52 enables the sealing members 57to compress the stack of the steel plates of the stator core 52 inwardlyin the axial direction. In other words, the sealing members 57 work tofirmly retain the stack of the steel plates of the stator core 52. Inthis embodiment, the inner peripheral surface of the stator core 52 isnot sealed using resin, but however, the whole of the stator core 52including the inner peripheral surface may be sealed using resin.

In a case where the rotating electrical machine 10 is used as a powersource for a vehicle, the sealing members 57 are preferably made of ahigh heat-resistance fluororesin, epoxy resin, PPS resin, PEEK resin,LCP resin, silicone resin, PAI resin, or PI resin. In terms of a linearcoefficient expansion to minimize breakage of the sealing members 57 dueto an expansion difference, the sealing members 57 are preferably madeof the same material as that of an outer film of the conductors of thestator winding 51. The silicone resin whose linear coefficient expansionis twice or more those of other resins is preferably excluded from thematerial of the sealing members 57. In a case of electrical products,such as electric vehicles equipped with no combustion engine, PPO resin,phenol resin, or FRP resin which resists 180° C. may be used, except infields where an ambient temperature of the rotating electrical machineis expected to be lower than 100° C.

The degree of torque outputted by the rotating electrical machine 10 isusually proportional to the degree of magnetic flux. In a case where astator core is equipped with teeth, a maximum amount of magnetic flux inthe stator core is restricted depending upon the saturation magneticflux density in the teeth, while in a case where the stator core is notequipped with teeth, the maximum amount of magnetic flux in the statorcore is not restricted. Such a structure is, therefore, useful forincreasing an amount of electrical current delivered to the statorwinding 51 to increase the degree of torque produced by the rotatingelectrical machine 10.

This embodiment employs the slot-less structure in which the stator 50is not equipped with teeth, thereby resulting in a decrease ininductance of the stator 50. Specifically, a stator of a typicalrotating electrical machine in which conductors are disposed in slotsisolated by teeth from each other has an inductance of approximately 1mH, while the stator 50 in this embodiment has a decreased inductance of5 to 60 μH. The rotating electrical machine 10 in this embodiment is ofan outer rotor type, but has a decreased inductance of the stator 50 todecrease a mechanical time constant Tm. In other words, the rotatingelectrical machine 10 is capable of outputting a high degree of torqueand designed to have a decreased value of the mechanical time constantTm. If inertia is defined as J, inductance is defined as L, torqueconstant is defined as Kt, and back electromotive force constant isdefined as Ke, the mechanical time constant Tm is calculated accordingto the equation of Tm=(J×L)/(Kt×Ke). This shows that a decrease ininductance L will result in a decrease in mechanical time constant Tm.

Each of the conductor groups 81 arranged radially outside the statorcore 52 is made of a plurality of conductors 82 whose transverse sectionis of a flattened rectangular shape and which are disposed on oneanother in the radial direction of the stator core 52. Each of theconductors 82 is oriented to have a transverse section meeting arelation of radial dimension <circumferential dimension. This causeseach of the conductor groups 81 to be thin in the radial direction. Aconductive region of the conductor group 81 also extends inside a regionoccupied by teeth of a typical stator. This creates a flattenedconductive region structure in which a sectional area of each of theconductors 82 is increased in the circumferential direction, therebyalleviating a risk that the amount of thermal energy may be increased bya decrease in sectional area of a conductor arising from flattening ofthe conductor. A structure in which a plurality of conductors arearranged in the circumferential direction and connected in parallel toeach other is usually subjected to a decrease in sectional area of theconductors by a thickness of a coated layer of the conductors, buthowever, has beneficial advantages obtained for the same reasons asdescribed above. In the following discussion, each of the conductorgroups 81 or each of the conductors 82 will also be referred to as aconductive member.

The stator 50 in this embodiment is, as described already, designed tohave no slots, thereby enabling the stator winding 51 to be designed tohave a conductive region of an entire circumferential portion of thestator 50 which is larger in size than a non-conductive regionunoccupied by the stator winding 51 in the stator 50. In typicalrotating electrical machines for vehicles, a ratio of the conductiveregion/the non-conductive region is usually one or less. In contrast,this embodiment has the conductor groups 81 arranged to have theconductive region substantially identical in size with or larger in sizethan the non-conductive region. If the conductor region, as illustratedin FIG. 10, occupied by the conductor 82 (i.e., the straight section 83which will be described later in detail) in the circumferentialdirection is defined as WA, and a conductor-to-conductor region that isan interval between a respective adjacent two of the conductors 82 isdefined as WB, the conductor region WA is larger in size than theconductor-to-conductor region WB in the circumferential direction.

The conductor group 81 of the stator winding 51 has a thickness in theradial direction thereof which is smaller than a circumferential widthof a portion of the stator winding 51 which lies in a region of onemagnetic pole and serves as one of the phases of the stator winding 51.In the structure in which each of the conductor groups 81 is made up ofthe two conductors 82 stacked in the form of two layers lying on eachother in the radial direction, and the two conductor groups 81 arearranged in the circumferential direction within a region of onemagnetic pole for each phase, a relation of Tc×2<Wc×2 is met where Tc isthe thickness of each of the conductors 82 in the radial direction, andWe is the width of each of the conductors 82 in the circumferentialdirection. In another structure in which each of the conductor groups 81is made up of the two conductors 82, and each of the conductor groups 81lies within the region of one magnetic pole for each phase, a relationof Tc×2<Wc is preferably met. In other words, in the stator winding 51which is designed to have conductor portions (i.e., the conductor groups81) arranged at a given interval away from each other in thecircumferential direction, the thickness of each conductor portion(i.e., the conductor group 81) in the radial direction is set smallerthan the width of a portion of the stator winding 51 lying in the regionof one magnetic pole for each phase in the circumferential direction.

In other words, each of the conductors 82 is preferably shaped to havethe thickness Tc in the radial direction which is smaller than the widthWc in the circumferential direction. The thickness 2Tc of each of theconductor groups 81 each made of a stack of the two conductors 82 in theradial direction is preferably smaller than the width Wc of each of theconductor groups 81 in the circumferential direction.

The degree of torque produced by the rotating electrical machine 10 issubstantially inversely proportional to the thickness of the stator core52 in the radial direction. The conductor groups 81 arranged radiallyoutside the stator core 52 are, as described above, designed to have thethickness decreased in the radial direction. This design is useful inincreasing the degree of torque outputted by the rotating electricalmachine 10. This is because a distance between the magnet unit 42 of therotor 40 and the stator core 52 (i.e., a distance in which there is noiron) may be decreased to decrease the magnetic resistance. This enablesinterlinkage magnetic flux in the stator core 52 produced by thepermanent magnets to be increased to enhance the torque.

The decrease in thickness of the conductor groups 81 facilitates theease with which a magnetic flux leaking from the conductor groups 81 iscollected in the stator core 52, thereby preventing the magnetic fluxfrom leaking outside the stator core 52 without being used for enhancingthe torque. This avoids a drop in magnetic force arising from theleakage of the magnetic flux and increases the interlinkage magneticflux in the stator core 52 produced by the permanent magnets, therebyenhancing the torque.

Each of the conductors 82 is made of a coated conductor formed bycovering the surface of the conductor body 82 a with the coating 82 b.The conductors 82 stacked on one another in the radial direction are,therefore, insulated from each other. Similarly, the conductors 82 areinsulated from the stator core 52. The insulating coating 82 b may be acoating of each wire 86, as will be described later in detail, in a casewhere each wire 86 is made of wire with a self-bonded coating or may bemade by an additional insulator disposed on a coating of each wire 86.Each phase winding made of the conductors 82 is insulated by the coating82 b except an exposed portion thereof for joining purposes. The exposedportion includes, for example, an input or an output terminal or aneutral point in a case of a star connection. The conductor groups 81arranged adjacent each other in the radial direction are firmly adheredto each other using resin or self-bonding coated wire, therebyminimizing a risk of insulation breakdown, mechanical vibration, ornoise caused by rubbing of the conductors 82.

In this embodiment, the conductor body 82 a is made of a collection of aplurality of wires 86. Specifically, the conductor body 82 a is, as canbe seen in FIG. 13, made of a strand of the twisted wires 86. Each ofthe wires 86 is, as can be seen in FIG. 14, made of a bundle of aplurality of thin conductive fibers 87. For instance, each of the wires86 is made of a complex of CNT (carbon nanotube) fibers. The CNT fibersinclude boron-containing microfibers in which at least a portion ofcarbon is substituted with boron. Instead of the CNT fibers that arecarbon-based microfibers, vapor grown carbon fiber (VGCF) may be used,but however, the CNT fiber is preferable. The surface of the wire 86 iscovered with a layer of insulating polymer, such as enamel. The surfaceof the wire 86 is preferably covered with an enamel coating, such aspolyimide coating or amide-imide coating.

The conductors 82 constitute n-phase windings of the stator winding 51.The wires 86 of each of the conductors 82 (i.e., the conductor body 82a) are placed in contact with each other. Each of the conductors 82 hasone of more portions which are formed by twisting the wires 86 anddefine one or more portions of a corresponding one of thephase-windings. A resistance value between the twisted wires 86 islarger than that of each of the wires 86. In other words, the respectiveadjacent two wires 86 have a first electrical resistivity in a directionin which the wires 86 are arranged adjacent each other. Each of thewires 86 has a second electrical resistivity in a lengthwise directionof the wire 86. The first electrical resistivity is larger than thesecond electrical resistivity. Each of the conductors 82 may be made ofan assembly of wires, i.e., the twisted wires 86 covered with insulatingmembers whose first electrical resistivity is very high. The conductorbody 82 a of each of the conductors 82 is made of a strand of thetwisted wires 86.

The conductor body 82 a is, as described above, made of the twistedwires 86, thereby reducing an eddy current created in each of the wires86, which reduces an eddy current in the conductor body 82 a. Each ofthe wires 86 is twisted, thereby causing each of the wires 86 to haveportions where directions of applied magnetic field are opposite eachother, which cancels a back electromotive force. This results in areduction in the eddy current. Particularly, each of the wires 86 ismade of the conductive fibers 87, thereby enabling the conductive fibers87 to be thin and also enabling the number of times the conductivefibers 87 are twisted to be increased, which enhances the reduction ineddy current.

How to insulate the wires 86 from each other is not limited to the abovedescribed use of the polymer insulating layer, but the contactresistance may be used to resist a flow of current between the wires 86.In other words, the above beneficial advantage is obtained by adifference in potential arising from a difference between the resistancebetween the twisted wires 86 and the resistance of each of the wires 86as long as the resistance between the wires 86 is larger than that ofeach of the wires 86. For instance, the contact resistance may beincreased by using production equipment for the wires 86 and productionequipment for the stator 50 (i.e., an armature) of the rotatingelectrical machine 10 as discrete devices to cause the wires 86 to beoxidized during a transport time or a work interval.

Each of the conductors 82 is, as described above, of a low-profile orflattened rectangular shape in cross section. The more than oneconductors 82 are arranged in the radial direction. Each of theconductors 82 is made of a strand of the wires 86 each of which isformed by a self-bonding coating wire equipped with, for example, afusing or bonding layer or an insulating layer and which are twistedwith the bonding layers fused together. Each of the conductors 82 mayalternatively be made by forming twisted wires with no bonding layer ortwisted self-bonding coating wires into a desired shape using syntheticresin. The insulating coating 82 b of each of the conductors 82 may havea thickness of 80 μm to 100 μm which is larger than that of a coating oftypical wire (i.e., 5 μm to 40 μm). In this case, a required degree ofinsulation between the conductors 82 is achieved even if no insulatingsheet is interposed between the conductors 82.

It is also advisable that the insulating coating 82 b be higher indegree of insulation than the insulating layer of the wire 86 to achieveinsulation between the phase windings. For instance, the polymerinsulating layer of the wire 86 has a thickness of, for example, 5 μm.In this case, the thickness of the insulating coating 82 b of theconductor 82 is preferably selected to be 80 μm to 100 μm to achieve theinsulation between the phase windings.

Each of the conductors 82 may alternatively be made of a bundle of theuntwisted wires 86. In brief, each of the conductors 82 may be made of abundle of the wires 86 whose entire lengths are twisted, whose portionsare twisted, or whose entire lengths are untwisted. Each of theconductors 82 constituting the conductor portion is, as described above,made of a bundle of the wires 86. The resistance between the wires 86 islarger than that of each of the wires 86.

The conductors 82 are each bent and arranged in a given pattern in thecircumferential direction of the stator winding 51, thereby forming thephase-windings of the stator winding 51. The stator winding 51, asillustrated in FIG. 12, includes the coil side portion 53 and the coilends 54 and 55. The conductors 82 have the straight sections 83 whichextend straight in the axial direction of the stator winding 51 and formthe coil side portion 53. The conductors 82 have the turns 84 which arearranged outside the coil side portion 53 in the axial direction andform the coil ends 54 and 55. Each of the conductor 82 is made of awave-shaped string of conductor formed by alternately arranging thestraight sections 83 and the turns 84. The straight sections 83 arearranged to face the magnet unit 42 in the radial direction. Thestraight sections 83 are arranged at a given interval away from eachother and joined together using the turns 84 located outside the magnetunit 42 in the axial direction. The straight sections 83 correspond to amagnet facing portion.

In this embodiment, the stator winding 51 is shaped in the form of anannular distributed winding. In the coil side portion 53, the straightsections 83 are arranged at an interval away from each other whichcorresponds to each pole pair of the magnet unit 42 for each phase. Ineach of the coil ends 54 and 55, the straight sections 83 for each phaseare joined together by the turn 84 which is of a V-shape. The straightsections 83 which are paired for each pole pair are opposite to eachother in a direction of flow of electrical current. A respective two ofthe straight sections 83 which are joined together by each of the turns84 are different between the coil end 54 and the coil end 55. The jointsof the straight sections 83 by the turns 84 are arranged in thecircumferential direction on each of the coil ends 54 and 55 to completethe stator winding in a hollow cylindrical shape.

More specifically, the stator winding 51 is made up of two pairs of theconductors 82 for each phase. The stator winding 51 is equipped with afirst three-phase winding set including the U-phase winding, the V-phasewinding, and the W-phase winding and a second three-phase phase windingset including the X-phase winding, the Y-phase winding, and the Z-phasewinding. The first three-phase phase winding set and the secondthree-phase winding set are arranged adjacent each other in the radialdirection in the form of two layers. If the number of phases of thestator winding 51 is defined as S (i.e., 6 in this embodiment), thenumber of the conductors 82 for each phase is defined as m, 2×S×m=2Smconductors 82 are used for each pole pair in the stator winding 51. Therotating electrical machine in this embodiment is designed so that thenumber of phases S is 6, the number m is 4, and 8 pole pairs are used.6×4×8=192 conductors 82 are arranged in the circumferential direction ofthe stator core 52.

The stator winding 51 in FIG. 12 is designed to have the coil sideportion 53 which has the straight sections 82 arranged in the form oftwo overlapping layers disposed adjacent each other in the radialdirection. Each of the coil ends 54 and 55 has a respective two of theturns 84 which extend from the radially overlapping straight sections 82in opposite circumferential directions. In other words, the conductors82 arranged adjacent each other in the radial direction are opposite toeach other in direction in which the turns 84 extend except for ends ofthe stator winding 51.

A winding structure of the conductors 82 of the stator winding 51 willbe described below in detail. In this embodiment, the conductors 82formed in the shape of a wave winding are arranged in the form of aplurality of layers (e.g., two layers) disposed adjacent or overlappingeach other in the radial direction. FIGS. 15(a) and 15(b) illustrate thelayout of the conductors 82 which form the n^(th) layer. FIG. 15(a)shows the configurations of the conductor 82, as the side of the statorwinding 51 is viewed. FIG. 15(b) shows the configurations of theconductors 82 as viewed in the axial direction of the stator winding 51.In FIGS. 15(a) and 15(b), locations of the conductor groups 81 areindicated by symbols D1, D2, D3, . . . , and D9. For the sake ofsimplicity of disclosure, FIGS. 15(a) and 15(b) show only threeconductors 82 which will be referred to herein as the first conductor82_A, the second conductor 82_B, and the third conductor 82_C.

The conductors 82_A to 82_C have the straight sections 83 arranged at alocation of the n^(th) layer, in other words, at the same position inthe circumferential direction. Every two of the straight sections 82which are arranged at 6 pitches (corresponding to 3×m pairs) away fromeach other are joined together by one of the turns 84. In other words,in the conductors 82_A to 82_C, an outermost two of the seven straightsections 83 arranged in the circumferential direction of the statorwinding 51 on the same circle defined about the center of the rotor 40are joined together using one of the turns 84. For instance, in thefirst conductor 82_A, the straight sections 83 placed at the locationsD1 and D7 are joined together by the inverse V-shaped turn 84. Theconductors 82_B and 82_C are arranged at an interval equivalent to aninterval between a respective adjacent two of the straight sections 83away from each other in the circumferential direction at the location ofthe n^(th) layer. In this layout, the conductors 82_A to 82_C are placedat a location of the same layer, thereby resulting in a risk that theturns 84 thereof may physically interfere with each other. In order toalleviate such a risk, each of the turns 84 of the conductors 82_A to82_C in this embodiment is shaped to have an interference avoidingportion formed by offsetting a portion of the turn 84 in the radialdirection.

Specifically, the turn 84 of each of the conductors 82_A to 82_Cincludes the slant portion 84 a, the head portion 84 b, the slantportion 84 c, and the return portion 84 d. The slant portion 84 aextends in the circumferential direction of the same circle (which willalso be referred to as a first circle). The head portion 84 extends fromthe slant portion 84 a radially inside the first circle (i.e., upward inFIG. 15(b)) to reach another circle (which will also be referred to as asecond circle). The slant portion 84 c extends in the circumferentialdirection of the second circle. The return portion 84 d returns from thesecond circle back to the first circle. The head portion 84 b, the slantportion 84 c, and the return portion 84 d define the interferenceavoiding portion. The slant portion 84 c may be arranged radiallyoutside the slant portion 84 a.

In other words, each of the conductors 82_A to 82_C has the turn 84shaped to have the slant portion 84 a and the slant portion 84 c whichare arranged on opposite sides of the head portion 84 b at the center inthe circumferential direction. The locations of the slant portions 84 aand 84 b are different from each other in the radial direction (i.e., adirection perpendicular to the drawing of FIG. 15(a) or a verticaldirection in FIG. 15(b)). For instance, the turn 84 of the firstconductor 82_A is shaped to extend from the location D1 on the n^(th)layer in the circumferential direction, be bent at the head portion 84 bthat is the center of the circumferential length of the turn 84 in theradial direction (e.g., radially inwardly), be bent again in thecircumferential direction, extend again in the circumferentialdirection, and then be bent at the return portion 84 d in the radialdirection (e.g., radially outwardly) to reach the location D7 on then^(th) layer.

With the above arrangements, the slant portions 84 a of the conductors82_A to 82_C are arranged vertically or downward in the order of thefirst conductor 82_A, the second conductor 82_B, and the third conductor82_C. The head portions 84 b change the order of the locations of theconductors 82_A to 82_C in the vertical direction, so that the slantportions 84 c are arranged vertically or downward in the order of thethird conductor 82_3, the second conductor 82_B, and the first conductor82_A. This layout achieves an arrangement of the conductors 82_A to 82_Cin the circumferential direction without any physical interference witheach other.

In the structure wherein the conductors 82 are laid to overlap eachother in the radial direction to form the conductor group 81, the turns84 leading to a radially innermost one and a radially outermost one ofthe straight sections 83 forming the two or more layers are preferablylocated radially outside the straight sections 83. In a case where theconductors 83 forming the two or more layers are bent in the same radialdirection near boundaries between ends of the turns 84 and the straightsections 83, the conductors 83 are preferably shaped not to deterioratethe insulation therebetween due to physical interference of theconductors 83 with each other.

In the example of FIGS. 15(a) and 15(b), the conductors 82 laid on eachother in the radial direction are bent radially at the return portions84 d of the turns 84 at the location D7 to D9. It is advisable that theconductor 82 of the n^(th) layer and the conductor 82 of the n+1^(th)layer be bent, as illustrated in FIG. 16, at radii of curvaturedifferent from each other. Specifically, the radius of curvature R1 ofthe conductor 82 of the n^(th) layer is preferably selected to besmaller than the radius of curvature R2 of the conductor 82 of then+1^(th) layer.

Additionally, radial displacements of the conductor 82 of the n^(th)layer and the conductor 82 of the n+1^(th) layer are preferably selectedto be different from each other. If the amount of radial displacement ofthe conductor 82 of the n^(th) layer is defined as S1, and the amount ofradial displacement of the conductor 82 of the n+1^(th) layer locatedradially outside the nth layer defined as S2, the amount of radialdisplacement S1 is preferably selected to be greater than the amount ofradial displacement S2.

The above layout of the conductors 82 eliminates the risk ofinterference with each other, thereby ensuring a required degree ofinsulation between the conductors 82 even when the conductors 82 laid oneach other in the radial direction are bent in the same direction.

The structure of the magnet unit 42 of the rotor 40 will be describedbelow. In this embodiment, the magnet unit 42 is made of permanentmagnets in which a remanent flux density Br=1.0T, and an intrinsiccoercive force Hcj=400 kA/m. The permanent magnets used in thisembodiment are implemented by sintered magnets formed by sinteringgrains of magnetic material and compacting them into a given shape andhave the following specifications. The intrinsic coercive force Hcj on aJ-H curve is 400 kA/m or more. The remanent flux density Br on the J-Hcurve is 1.0T or more. Magnets designed so that when 5,000 to 10,000ATis applied thereto by phase-to-phase excitation, a magnetic distancebetween paired poles, i.e., between a N-pole and an S-pole, in otherwords, of a path in which a magnetic flux flows between the N-pole andthe S-pole, a portion lying in the magnet has a length of 25 mm may beused to meet a relation of Hcj=10000A without becoming demagnetized.

In other words, the magnet unit 42 is engineered so that a saturationmagnetic flux density Js is 1.2T or more, a grain size is 10 μm or less,and a relation of Js×a≥1.0T is met where a is an orientation ratio.

The magnet unit 42 will be additionally described below. The magnet unit42 (i.e., magnets) has a feature that Js meets a relation of2.15T≥Js≥1.2T. In other words, magnets used in the magnet unit 42 may beFeNi magnets having NdFe11TiN, Nd2Fe14B, Sm2Fe17N3, or L10 crystals.Note that samarium-cobalt magnets, such as SmCoS, FePt, Dy2Fe14B, orCoPt magnets can not be used. When magnets in which high Jscharacteristics of neodymium are slightly lost, but a high degree ofcoercive force of Dy is ensured using the heavy rare earth dysprosium,like in homotopic compounds, such as Dy2Fe14B and Nd2Fe14B, sometimesmeets a relation of 2.15T≥Js≥1.2T, they may be used in the magnet unit42. Such a type of magnet will also be referred to herein as[Nd1−xDyx]2Fe14B]. Further, a magnet contacting different types ofcompositions, in other words, a magnet made from two or more types ofmaterials, such as FeNi and Sm2Fe17N3, may be used to meet a relation of2.15T≥Js≥1.2T. A mixed magnet made by adding a small amount of, forexample, Dy2Fe14B in which Js<1T to an Nd2Fe14B magnet in which Js=1.6T,meaning that Js is sufficient to enhance the coercive force, may also beused to meet a relation of 2.15T≥Js≥1.2T.

In use of the rotating electrical machine at a temperature outside atemperature range of human activities which is higher than, for example,60° C. exceeding temperatures of deserts, for example, within apassenger compartment of a vehicle where the temperature may rise to 80°C. in summer, the magnet preferably contains FeNi or Sm2Fe17N3components which are less dependent on temperature. This is becausemotor characteristics are greatly changed by temperature-dependentfactors thereof in motor operations within a range of approximately −40°which is within a range experienced by societies in Northern Europe to60° C. or more experienced in desert region or at 180 to 240° C. that isa heat resistance temperature of the enamel coating, which leads to adifficulty in achieving a required control operation using the samemotor driver. The use of FeNi containing the above described L10crystals or Sm2Fe17N3 magnets will result in a decrease in load on themotor driver because characteristics thereof have temperature-dependentfactors lower than half that of Nd2Fe14B magnets.

Additionally, the magnet unit 42 is engineered to use the abovedescribed magnet mixing so that a particle size of fine powder beforebeing magnetically oriented is lower than or equal to 10 μm and higherthan or equal to a size of single-domain particles. The coercive forceof a magnet is usually increased by decreasing the size of poweredparticles thereof to a few hundred nm. In recent years, smallestpossible particles have been used. If the particles of the magnet aretoo small, the BHmax (i.e., the maximum energy product) of the magnetwill be decreased due to oxidization thereof. It is, thus, preferablethat the particle size of the magnet is higher than or equal to the sizeof the single-domain particles. The particle size being only up to thesize of the single-domain particles is known to increase the coerciveforce of the magnet. The particle size, as referred to herein, refers tothe diameter or size of fine powdered particles in a magneticorientation operation in production processes of magnets.

Each of the first magnet 91 and the second magnet 92 of the magnet unit42 are made of sintered magnets formed by firing or heating magneticpowder at high temperatures and compacting it. The sintering is achievedso as to meet conditions where the saturation magnetization Js of themagnet unit 42 is 1.2T (Tesla) or more, the particle size of the firstmagnet 91 and the second magnet 92 is 10 μm or less, and Js×a is higherthan or equal to 1.0T (Tesla) where a is an orientation ratio. Each ofthe first magnet 91 and the second magnet 92 are also sintered to meetthe following conditions. By performing the magnetic orientation in themagnetic orientation operation in the production processes of the firstmagnet 91 and the second magnet 92, they have an orientation ratiodifferent to the definition of orientation of magnetic force in amagnetization operation for isotropic magnets. The magnet unit 42 inthis embodiment is designed to have the saturation magnetization Js morethan or equal to 1.2T and the orientation ratio a of the first magnet 91and the second magnet 92 which is high to meet a relation ofJr≥Js×a≥1.0T. The orientation ratio a, as referred to herein, is definedin the following way. If each of the first magnet 91 and the secondmagnet 92 has six easy axes of magnetization, five of the easy axes ofmagnetization are oriented in the same direction A10, and a remainingone of the easy axes of magnetization is oriented in the direction B10angled at 90 degrees to the direction A10, then a relation of a=⅚ ismet. Alternatively, if each of the first magnet 91 and the second magnet92 has six easy axes of magnetization, five of the easy axes ofmagnetization are oriented in the same direction A10, and a remainingone of the easy axes of magnetization is oriented in the direction B10angled at 45 degrees to the direction A10, then a relation ofa=(5+0.707)/6 is met since a component oriented in the direction A10 isexpressed by cos 45°=0.707. The first magnet 91 and the second magnet 92in this embodiment are, as described above, each made using sinteringtechniques, but however, they may be produced in another way as long asthe above conditions are satisfied. For instance, a method of forming anMQ3 magnet may be used.

In this embodiment, permanent magnets are used which are magneticallyoriented to control the easy axis of magnetization thereof, therebyenabling a magnetic circuit length within the magnets to be longer thanthat within typical linearly oriented magnets which produces a magneticflux density of 1.0T or more. In other words, the magnetic circuitlength for one pole pair in the magnets in this embodiment may beachieved using magnets with a small volume. Additionally, a range ofreversible flux loss in the magnets is not lost when subjected to severehigh temperatures, as compared with use of typical linearly orientedmagnets. The inventors of this application have found thatcharacteristics similar to those of anisotropic magnets are obtainedeven using prior art magnets.

The easy axis of magnetization represents a crystal orientation in whicha crystal is easy to magnetize in a magnet. The orientation of the easyaxis of magnetization in the magnet, as referred to herein, is adirection in which an orientation ratio is 50% or more where theorientation ratio indicates the degree to which easy axes ofmagnetization of crystals are aligned with each other or a direction ofan average of magnetic orientations in the magnet.

The magnet unit 42 is, as clearly illustrated in FIGS. 8 and 9, of anannular shape and arranged inside the magnet holder 41 (specifically,radially inside the cylinder 43). The magnet unit 42 is equipped withthe first magnets 91 and the second magnets 92 which are each made of apolar anisotropic magnet. Each of the first magnets 91 and each of thesecond magnets 92 are different in polarity from each other. The firstmagnets 91 and the second magnets 92 are arranged alternately in thecircumferential direction of the magnet unit 42. Each of the firstmagnets 91 is engineered to have a portion creating an N-pole near thestator winding 51. Each of the second magnets 92 is engineered to have aportion creating an S-pole near the stator winding 51. The first magnets91 and the second magnets 92 are each made of, for example, a permanentrare earth magnet, such as a neodymium magnet.

Each of the magnets 91 and 92 is engineered to have a direction ofmagnetization (which will also be referred to below as a magnetizationdirection) which extends in an annular shape in between a d-axis (i.e.,a direct-axis) and a q-axis (i.e., a quadrature-axis) in a known d-qcoordinate system where the d-axis represents the center of a magneticpole, and the q-axis represents a magnetic boundary between the N-poleand the S-pole, in other words, where a density of magnetic flux is zeroTesla. In each of the magnets 91 and 92, the magnetization direction isoriented in the radial direction of the annular magnet unit 42 close tothe d-axis and also oriented in the circumferential direction of theannular magnet unit 42 closer to the q-axis. This layout will also bedescribed below in detail. Each of the magnets 91 and 92, as can be seenin FIG. 9, includes a first portion 250 and two second portions 260arranged on opposite sides of the first portion 250 in thecircumferential direction of the magnet unit 42. In other words, thefirst portion 250 is located closer to the d-axis than the secondportions 260 are. The second portions 260 are arranged closer to theq-axis than the first portion 250 is. The direction in which the easyaxis of magnetization 300 extends in the first portion 250 is orientedmore parallel to the d-axis than the direction in which the easy axis ofmagnetization 310 extends in the second portions 260. In other words,the magnet unit 42 is engineered so that an angle θ11 which the easyaxis of magnetization 300 in the first portion 250 makes with the d-axisis selected to be smaller than an angle θ12 which the easy axis ofmagnetization 310 in the second portion 260 makes with the q-axis.

More specifically, if a direction from the stator 50 (i.e., an armature)toward the magnet unit 42 on the d-axis is defined to be positive, theangle θ11 represents an angle which the easy axis of magnetization 300makes with the d-axis. Similarly, if a direction from the stator 50(i.e., an armature) toward the magnet unit 42 on the q-axis is definedto be positive, the angle θ12 represents an angle which the easy axis ofmagnetization 310 makes with the q-axis. In this embodiment, each of theangle θ11 and the angle θ12 is set to be 90° or less. Each of the easyaxes of magnetization 300 and 310, as referred to herein, is defined inthe following way. If in each of the magnets 91 and 92, a first one ofthe easy axes of magnetization is oriented in a direction A11, and asecond one of the easy axes of magnetization is oriented in a directionB11, an absolute value of cosine of an angle θ which the direction A11and the direction B11 make with each other (i.e., |cos θ|) is defined asthe easy axis of magnetization 300 or the easy axis of magnetization310.

The magnets 91 are different in easy axis of magnetization from themagnets 92 in regions close to the d-axis and the q-axis. Specifically,in the region close to the d-axis, the direction of the easy axis ofmagnetization is oriented approximately parallel to the d-axis, while inthe region close to the q-axis, the direction of the easy axis ofmagnetization is oriented approximately perpendicular to the q-axis.Annular magnetic paths are created according to the directions of easyaxes of magnetization. In each of the magnets 91 and 92, the easy axisof magnetization in the region close to the d-axis may be orientedparallel to the d-axis, while the easy axis of magnetization in theregion close to the q-axis may be oriented perpendicular to the q-axis.

Each of the magnets 91 and 92 is shaped to have a stator-side outerperipheral surface facing the stator 50 (i.e., a lower surface viewed inFIG. 9) and a q-axis-side outer peripheral surface facing the q-axis inthe circumferential direction. The stator-side outer peripheral surfaceand the q-axis-side outer peripheral surface function as magnetic fluxinput and output surfaces that are magnetic flux acting surfaces intoand from which magnetic flux flows, respectively. The magnetic paths areeach created to extend between the magnetic flux acting surfaces (i.e.,between the stator-side outer peripheral surface and the q-axis-sideouter peripheral surface).

In the magnet unit 42, a magnetic flux flows in an annular shape betweena respective adjacent two of the N-poles and the S-poles of the magnets91 and 92, so that each of the magnetic paths has an increased length,as compared with, for example, radial anisotropic magnets. Adistribution of the magnetic flux density will, therefore, exhibit ashape similar to a sine wave illustrated in FIG. 17. This facilitatesconcentration of magnetic flux around the center of the magnetic poleunlike a distribution of magnetic flux density of a radial anisotropicmagnet demonstrated in FIG. 18 as a comparative example, therebyenabling the degree of torque produced by the rotating electricalmachine 10 to be increased. It has also been found that the magnet unit42 in this embodiment has the distribution of the magnetic flux densitydistinct from that of a typical Halbach array magnet. In FIGS. 17 and18, a horizontal axis indicates the electrical angle, while a verticalaxis indicates the magnetic flux density. 90° on the horizontal axisrepresents the d-axis (i.e., the center of the magnetic pole). 0° and180° on the horizontal axis represent the q-axis.

Accordingly, the above described structure of each of the magnets 91 and92 functions to enhance the magnet magnetic flux thereof on the d-axisand reduce a change in magnetic flux near the q-axis. This enables themagnets 91 and 92 to be produced which have a smooth change in surfacemagnetic flux from the q-axis to the d-axis on each magnetic pole

The sine wave matching percentage in the distribution of the magneticflux density is preferably set to, for example, 40% or more. Thisimproves the amount of magnetic flux around the center of a waveform ofthe distribution of the magnetic flux density as compared with aradially oriented magnet or a parallel oriented magnet in which the sinewave matching percentage is approximately 30%. By setting the sine wavematching percentage to be 60% or more, the amount of magnetic fluxaround the center of the waveform is improved, as compared with aconcentrated magnetic flux array, such as the Halbach array.

In the radial anisotropic magnet demonstrated in FIG. 18, the magneticflux density changes sharply near the q-axis. The more sharp the changein magnetic flux density, the more an eddy current generating in thestator winding 51 will increase. The magnetic flux close to the statorwinding 51 also sharply changes. In contrast, the distribution of themagnetic flux density in this embodiment has a waveform approximating asine wave. A change in magnetic flux density near the q-axis is,therefore, smaller than that in the radial anisotropic magnet near theq-axis. This minimizes the generation of the eddy current.

The magnet unit 42 creates a magnetic flux oriented perpendicular to themagnetic flux acting surface 280 close to the stator 50 near the d-axis(i.e., the center of the magnetic pole) in each of the magnets 91 and92. Such a magnetic flux extends in an arc-shape farther away from thed-axis as leaving the magnetic flux acting surface 280 close to thestator 50. The more perpendicular to the magnetic flux acting surfacethe magnetic flux extends, the stronger the magnetic flux is. Therotating electrical machine 10 in this embodiment is, as describedabove, designed to shape each of the conductor groups 81 to have adecreased thickness in the radial direction, so that the radial centerof each of the conductor groups 81 is located close to the magneticflux-acting surface of the magnet unit 42, thereby causing the strongmagnetic flux to be applied to the stator 50 from the rotor 40.

The stator 50 has the cylindrical stator core 52 arranged radiallyinside the stator winding 51, that is, on the opposite side of thestator winding 51 to the rotor 40. This causes the magnetic fluxextending from the magnetic flux-acting surface of each of the magnets91 and 92 to be attracted by the stator core 52, so that it circulatesthrough the magnetic path partially including the stator core 52. Thisenables the orientation of the magnetic flux and the magnetic path to beoptimized.

Steps to assemble the bearing unit 20, the housing 30, the rotor 40, thestator 50, and the inverter unit 60 illustrated in FIG. 5 will bedescribed below as a production method of the rotating electricalmachine 10. The inverter unit 60 is, as illustrated in FIG. 6, equippedwith the unit base 61 and the electrical components 62. Operationprocesses including installation processes for the unit base 61 and theelectrical components 62 will be explained. In the following discussion,an assembly of the stator 50 and the inverter unit 60 will be referredto as a first unit. An assembly of the bearing unit 20, the housing 30,and the rotor 40 will be referred to as a second unit.

The production processes include:

a first step of installing he electrical components 62 radially insidethe unit base 61;

a second step of installing the unit base 61 radially inside the stator50 to make the first unit;

a third step of inserting the attaching portion 44 of the rotor 40 intothe bearing unit 20 installed in the housing 30 to make the second unit;

a fourth step of installing the first unit radially inside the secondunit; and

a fifth step of fastening the housing 30 and the unit base 61 together.The order in which the above steps are performed is the first step→thesecond step→the third step→the fourth step→the fifth step.

In the above production method, the bearing unit 20, the housing 30, therotor 40, the stator 50, and the inverter unit 60 are assembled as aplurality of sub-assemblies, and the sub-assemblies are assembled,thereby facilitating handling thereof and achieving completion ofinspection of each sub-assembly. This enables an efficient assembly lineto be established and thus facilitates multi-product productionplanning.

In the first step, a high thermal conductivity material is applied oradhered to at least one of the radial inside of the unit base 61 and theradial outside of the electrical components 62. Subsequently, theelectrical components may be mounted on the unit base 61. This achievesefficient transfer of heat, as generated by the semiconductor modules66, to the unit base 61.

In the third step, an insertion operation for the rotor 40 may beachieved with the housing 30 and the rotor 40 arranged coaxially witheach other. Specifically, the housing 30 and the rotor 40 are assembledwhile sliding one of the housing 30 and the rotor 40 along a jig whichpositions the outer peripheral surface of the rotor 40 (i.e., the outerperipheral surface of the magnetic holder 41) or the inner peripheralsurface of the rotor 40 (i.e., the inner peripheral surface of themagnet unit 42) with respect to, for example, the inner peripheralsurface of the housing 30. This achieves the assembly of heavy-weightparts without exertion of imbalanced load to the bearing unit 20. Thisresults in improvement of reliability in operation of the bearing unit20.

In the fourth step, the first unit and the second unit may be installedwhile being placed coaxially with each other. Specifically, the firstunit and the second unit are installed while sliding one of the firstunit and the second unit along a jig which positions the innerperipheral surface of the unit base 61 with respect to, for example, theinner peripheral surfaces of the rotor 40 and the attaching portion 44.This achieves the installation of the first and second units without anyphysical interference therebetween within a small clearance between therotor 40 and the stator 50, thereby eliminating risks of defects causedby the installation, such as physical damage to the stator winding 51 ordamage to the permanent magnets.

The above steps may alternatively be scheduled as the second step→thethird step→the fourth step→the fifth step→the first step. In this order,the delicate electrical components 62 are finally installed, therebyminimizing stress on the electrical components in the installationprocesses.

The structure of a control system for controlling an operation of therotating electrical machine 10 will be described below. FIG. 19 is anelectrical circuit diagram of the control system for the rotatingelectrical machine 10. FIG. 20 is a functional block diagram whichillustrates control steps performed by the controller 110.

FIG. 19 illustrates two sets of three-phase windings 51 a and 51 b. Thethree-phase winding 51 a includes a U-phase winding, a V-phase winding,and a W-phase winding. The three-phase winding 51 b includes an X-phasewinding, a Y-phase winding, and a Z-phase winding. The first inverter101 and the second inverter 102 are provided as electrical powerconverters for the three-phase windings 51 a and 51 b, respectively. Theinverters 101 and 102 are made of bridge circuits with as many upper andlower arms as there are the phase-windings. The current delivered to thephase windings of the stator winding 51 is regulated by turning on oroff switches (i.e., semiconductor switches) mounted on the upper andlower arms.

The dc power supply 103 and the smoothing capacitor 104 are connectedparallel to the inverters 101 and 102. The dc power supply 103 is madeof, for example, a plurality of series-connected cells. The switches ofthe inverters 101 and 102 correspond to the semiconductor modules 66 inFIG. 1. The capacitor 104 corresponds to the capacitor module 68 in FIG.1.

The controller 110 is equipped with a microcomputer made of a CPU andmemories and works to perform control energization by turning on or offthe switches of the inverters 101 and 102 using several types ofmeasured information measured in the rotating electrical machine 10 orrequests for a motor mode or a generator mode of the rotating electricalmachine 10. The controller 110 corresponds to the control device 77shown in FIG. 6. The measured information about the rotating electricalmachine 10 includes, for example, an angular position (i.e., anelectrical angle) of the rotor 40 measured by an angular positionsensor, such as a resolver, a power supply voltage (i.e., voltageinputted into the inverters) measured by a voltage sensor, andelectrical current delivered to each of the phase-windings, as measuredby a current sensor. The controller 110 produces and outputs anoperation signal to operate each of the switches of the inverters 101and 102. A request for electrical power generation is a request fordriving the rotating electrical machine 10 in a regenerative mode, forexample, in a case where the rotating electrical machine 10 is used as apower source for a vehicle.

The first inverter 101 is equipped with a series-connected part made upof an upper arm switch Sp and a lower arm switch Sn for each of thethree-phase windings: the U-phase winding, the V-phase winding, and theW-phase winding. The upper arm switches Sp are connected athigh-potential terminals thereof to a positive terminal of the dc powersupply 103. The lower arm switches Sn are connected at low-potentialterminals thereof to a negative terminal (i.e., ground) of the dc powersupply 103. Intermediate joints of the upper arm switches Sp and thelower arm switches Sn are connected to ends of the U-phase winding, theV-phase winding, and the W-phase winding. The U-phase winding, theV-phase winding, and the W-phase winding are connected in the form of astar connection (i.e., Y-connection). The other ends of the U-phasewinding, the V-phase winding, and the W-phase winding are connected witheach other at a neutral point.

The second inverter 102 is, like the first inverter 101, equipped with aseries-connected part made up of an upper arm switch Sp and a lower armswitch Sn for each of the three-phase windings: the X-phase winding, theY-phase winding, and the Z-phase winding. The upper arm switches Sp areconnected at high-potential terminals thereof to the positive terminalof the dc power supply 103. The lower arm switches Sn are connected atlow-potential terminals thereof to the negative terminal (i.e., ground)of the dc power supply 103. Intermediate joints of the upper armswitches Sp and the lower arm switches Sn are connected to ends of theX-phase winding, the Y-phase winding, and the Z-phase winding. TheX-phase winding, the Y-phase winding, and the Z-phase winding areconnected in the form of a star connection (i.e., Y-connection). Theother ends of the X-phase winding, the Y-phase winding, and the Z-phasewinding are connected with each other at a neutral point.

FIG. 20 illustrates a current feedback control operation to controlelectrical currents delivered to the U-phase winding, the V-phasewinding, and the W-phase winding and a current feedback controloperation to control electrical currents delivered to the X-phasewinding, the Y-phase winding, and the Z-phase winding. The controloperation for the U-phase winding, the V-phase winding, and the W-phasewinding will first be discussed.

In FIG. 20, the current command determiner 111 uses a torque-dq map todetermine current command values for the d-axis and the q-axis using atorque command value in the motor mode of the rotating electricalmachine 10 (which will also be referred to as a motor-mode torquecommand value), a torque command value in the generator mode of therotating electrical machine 10 (which will be referred to as agenerator-mode torque command value), and an electrical angular velocityω derived by differentiating an electrical angle θ with respect to time.The current command determiner 111 is shared between the U-, V-, andW-phase windings and the X-, Y-, and W-phase windings. Thegenerator-mode torque command value is a regenerative torque commandvalue in a case where the rotating electrical machine 10 is used as apower source of a vehicle.

The d-q converter 112 works to convert currents (i.e., three phasecurrents), as measured by current sensors mounted for the respectivephase windings, into a d-axis current and a q-axis current that arecomponents in a two-dimensional rotating Cartesian coordinate system inwhich a d-axis is defined as a direction of an axis of a magnetic fieldor field direction.

The d-axis current feedback control device 113 determines a commandvoltage for the d-axis as a manipulated variable for bringing the d-axiscurrent into agreement with the current command value for the d-axis ina feedback mode. The q-axis current feedback control device 114determines a command voltage for the q-axis as a manipulated variablefor bringing the q-axis current into agreement with the current commandvalue for the q-axis in a feedback mode. The feedback control devices113 and 114 calculates the command voltage as a function of a deviationof each of the d-axis current and the q-axis current from acorresponding one of the current command values using

PI feedback techniques.

The three-phase converter 115 works to convert the command values forthe d-axis and the q-axis into command values for the U-phase, V-phase,and W-phase windings. Each of the devices 111 to 115 is engineered as afeedback controller to perform a feedback control operation for afundamental current in the d-q transformation theory. The commandvoltages for the U-phase, V-phase, and W-phase windings are feedbackcontrol values.

The operation signal generator 116 uses the known triangle wave carriercomparison to produce operation signals for the first inverter 101 as afunction of the three-phase command voltages. Specifically, theoperation signal generator 116 works to produce switch operation signals(i.e., duty signals) for the upper and lower arms for the three-phasewindings (i.e., the U-, V-, and W-phase windings) under PWM controlbased on comparison of levels of signals derived by normalizing thethree-phase command voltages using the power supply voltage with a levelof a carrier signal, such as a triangle wave signal.

The same structure as described above is provided for the X-, Y-, andZ-phase windings. The d-q converter 122 works to convert currents (i.e.,three phase currents), as measured by current sensors mounted for therespective phase windings, into a d-axis current and a q-axis currentthat are components in the two-dimensional rotating Cartesian coordinatesystem in which the d-axis is defined as the direction of the axis ofthe magnetic field.

The d-axis current feedback control device 123 determines a commandvoltage for the d-axis. The q-axis current feedback control device 124determines a command voltage for the q-axis. The three-phase converter125 works to convert the command values for the d-axis and the q-axisinto command values for the X-phase, Y-phase, and Z-phase windings. Theoperation signal generator 126 produces operation signals for the secondinverter 102 as a function of the three-phase command voltages.Specifically, the operation signal generator 126 works to switchoperation signals (i.e., duty signals) for the upper and lower arms forthe three-phase windings (i.e., the X-, Y-, and Z-phase windings) basedon comparison of levels of signals derived by normalizing thethree-phase command voltages using the power supply voltage with a levelof a carrier signal, such as a triangle wave signal.

The driver 117 works to turn on or off the switches Sp and Sn in theinverters 101 and 102 in response to the switch operation signalsproduced by the operation signal generators 116 and 126.

Subsequently, a torque feedback control operation will be describedbelow. This operation is to increase an output of the rotatingelectrical machine 10 and reduce torque loss in the rotating electricalmachine 10, for example, in a high-speed and high-output range whereinoutput voltages from the inverters 101 and 102 rise. The controller 110selects one of the torque feedback control operation and the currentfeedback control operation and perform the selected one as a function ofan operating condition of the rotating electrical machine 10.

FIG. 21 shows the torque feedback control operation for the U-, V-, andW-phase windings and the torque feedback control operation for the X-,Y-, and Z-phase windings. In FIG. 21, the same reference numbers asemployed in FIG. 20 refer to the same parts, and explanation thereof indetail will be omitted here. The control operation for the U-, V-, andW-phase windings will be described first.

The voltage amplitude calculator 127 works to calculate a voltageamplitude command that is a command value of a degree of a voltagevector as a function of the motor-mode torque command value or thegenerator-mode torque command value for the rotating electrical machine10 and the electrical angular velocity ω derived by differentiating theelectrical angle θ with respect to time.

The torque calculator 128 a works to estimate a torque value in theU-phase, V-phase, or the W-phase as a function of the d-axis current andthe q-axis current converted by the d-q converter 112. The torquecalculator 128 a may be designed to calculate the voltage amplitudecommand using a map listing relations among the d-axis current, theq-axis current, and the voltage amplitude command.

The torque feedback controller 129 a calculates a voltage phase commandthat is a command value for a phase of the voltage vector as amanipulated variable for bringing the estimated torque value intoagreement with the motor-mode torque command value or the generator-modetorque command value in the feedback mode. Specifically, the torquefeedback controller 129 a calculates the voltage phase command as afunction of a deviation of the estimated torque value from themotor-mode torque command value or the generator-mode torque commandvalue using PI feedback techniques.

The operation signal generator 130 a works to produce the operationsignal for the first inverter 101 using the voltage amplitude command,the voltage phase command, and the electrical angle θ. Specifically, theoperation signal generator 130 a calculates the command values for thethree-phase windings based on the voltage amplitude command, the voltagephase command, and the electrical angle θ and then generates switchingoperation signals for the upper and lower arms for the three-phasewindings by means of PWM control based on comparison of levels ofsignals derived by normalizing the three-phase command voltages usingthe power supply voltage with a level of a carrier signal, such as atriangle wave signal.

The operation signal generator 130 a may alternatively be designed toproduce the switching operation signals using pulse pattern informationthat is map information about relations among the voltage amplitudecommand, the voltage phase command, the electrical angle θ, and theswitching operation signal, the voltage amplitude command, the voltagephase command, and the electrical angle θ.

The same structure as described above is provided for the X-, Y-, andZ-phase windings. The torque calculator 128 b works to estimate a torquevalue in the X-phase, Y-phase, or the Z-phase as a function of thed-axis current and the q-axis current converted by the d-q converter122.

The torque feedback controller 129 b calculates a voltage phase commandas a manipulated variable for bringing the estimated torque value intoagreement with the motor-mode torque command value or the generator-modetorque command value in the feedback mode. Specifically, the torquefeedback controller 129 b calculates the voltage phase command as afunction of a deviation of the estimated torque value from themotor-mode torque command value or the generator-mode torque commandvalue using PI feedback techniques.

The operation signal generator 130 b works to produce the operationsignal for the second inverter 102 using the voltage amplitude command,the voltage phase command, and the electrical angle θ. Specifically, theoperation signal generator 130 b calculates the command values for thethree-phase windings based on the voltage amplitude command, the voltagephase command, and the electrical angle θ and then generates theswitching operation signals for the upper and lower arms for thethree-phase windings by means of PWM control based on comparison oflevels of signals derived by normalizing the three-phase commandvoltages using the power supply voltage with a level of a carriersignal, such as a triangle wave signal. The driver 117 then works toturn on or off the switches Sp and Sn for the three-phase windings inthe inverters 101 and 102 in response to the switching operation signalsderived by the operation signal generators 130 a and 130 b.

The operation signal generator 130 b may alternatively be designed toproduce the switching operation signals using pulse pattern informationthat is map information about relations among the voltage amplitudecommand, the voltage phase command, the electrical angle θ, and theswitching operation signal, the voltage amplitude command, the voltagephase command, and the electrical angle θ.

The rotating electrical machine 10 has a risk that generation of anaxial current may result in electrical erosion in the bearing 21 or 22.For example, when the stator winding 51 is excited or de-excited inresponse to the switching operation, a small switching time gap (i.e.,switching unbalance) may occur, thereby resulting in distortion ofmagnetic flux, which leads to the electrical erosion in the bearings 21and 22 retaining the rotating shaft 11. The distortion of magnetic fluxdepends upon the inductance of the stator 50 and creates anelectromotive force oriented in the axial direction, which results indielectric breakdown in the bearing 21 or 22 to develop the electricalerosion.

In order to avoid the electrical erosion, this embodiment is engineeredto take three measures as discussed below. The first erosion avoidingmeasure is to reduce the inductance by designing the stator 50 to have acore-less structure and also to shape the magnetic flux in the magnetunit 42 to be smooth to minimize the electrical erosion. The seconderosion avoiding measure is to retain the rotating shaft in a cantileverform to minimize the electrical erosion. The third erosion avoidingmeasure is to unify the annular stator winding 51 and the stator core 52using molding techniques using a moulding material to minimize theelectrical erosion. The first to third erosion avoiding measures will bedescribed below in detail.

In the first erosion avoiding measure, the stator 50 is designed to haveno teeth in gaps between the conductor groups 81 in the circumferentialdirection. The sealing members 57 made of non-magnetic material arearranged in the gaps between the conductor groups 81 instead of teeth(iron cores) (see FIG. 10). This results in a decrease in inductance ofthe stator 50, thereby minimizing the distortion of magnetic flux causedby the switching time gap occurring upon excitation of the statorwinding 51 to reduce the electrical erosion in the bearings 21 and 22.The inductance on the d-axis is preferably less than that on the q-axis.

Additionally, each of the magnets 91 and 92 is magnetically oriented tohave the easy axis of magnetization which is directed in a region closeto the d-axis to be more parallel to the d-axis than that in a regionclose to the q-axis (see FIG. 9). This strengthens the magnetic flux onthe d-axis, thereby resulting in a smooth change in surface magneticflux (i.e., an increase or decrease in magnetic flux) from the q-axis tothe d-axis on each magnetic pole of the magnets 91 and 92. Thisminimizes a sudden voltage change arising from the switching imbalanceto avoid the electrical erosion.

In the second erosion avoiding measure, the rotating electrical machine10 is designed to have the bearings 21 and 22 located away from theaxial center of the rotor 40 toward one of the ends of the rotor 40opposed to each other in the axial direction thereof (see FIG. 2). Thisminimizes the risk of the electrical erosion as compared with a casewhere a plurality of bearings are arranged outside axial ends of arotor. In other words, in the structure wherein the rotor has endsretained by the bearings, generation of a high-frequency magnetic fluxresults in creation of a closed circuit extending through the rotor, thestator, and the bearings (which are arranged axially outside the rotor).This leads to a risk that the axial current may result in the electricalerosion in the bearings. In contrast, the rotor 40 are retained by theplurality of bearings 21 and 22 in the cantilever form, so that theabove closed circuit does not occur, thereby minimizing the electricalerosion in the bearings 21 and 22.

In addition to the above one-side layout of the bearings 21 and 22, therotating electrical machine 10 also has the following structure. In themagnet holder 41, the intermediate portion 45 extending in the radialdirection of the rotor 40 is equipped with the contact avoider whichaxially extends to avoid physical contact with the stator 50 (see FIG.2). This enables a closed circuit through which the axial current flowsthrough the magnet holder 41 to be lengthened to increase the resistancethereof. This minimizes the risk of the electrical erosion of thebearings 21 and 22.

The retainer 23 for the bearing unit 20 is secured to the housing 30 andlocated on one axial end side of the rotor 40, while the housing 30 andthe unit base 61 (i.e., a stator holder) are joined together on theother axial end of the rotor 40 (see FIG. 2). These arrangementsproperly achieve the structure in which the bearings 21 and 22 arelocated only on the one end of the length of the rotating shaft 11.Additionally, the unit base 61 is connected to the rotating shaft 11through the housing 30, so that the unit base 61 is located electricallyaway from the rotating shaft 11. An insulating member such as resin maybe disposed between the unit base 61 and the housing 30 to place theunit base 61 and the rotating shaft 11 electrically farther away fromeach other. This also minimizes the risk of the electrical erosion ofthe bearings 21 and 22.

The one-side layout of the bearings 21 and 22 in the rotating electricalmachine 10 in this embodiment decreases the axial voltage applied to thebearings 21 and 22 and also decreases the potential difference betweenthe rotor 40 and the stator 50. A decrease in the potential differenceapplied to the bearings 21 and 22 is, thus, achieved without use ofconductive grease in the bearings 21 and 22. The conductive greaseusually contains fine particles such as carbon particles, thus leadingto a risk of generation of acoustic noise. In order to alleviate theabove problem, this embodiment uses a non-conductive grease in thebearings 21 and 22 to minimize the acoustic noise in the bearings 21 and22. For instance, in a case where the rotating electrical machine 10 isused with an electrical vehicle, it is usually required to take ameasure to eliminate the acoustic noise. This embodiment is capable ofproperly taking such a measure.

In the third erosion avoiding measure, the stator winding 51 and thestator core 52 are unified together using a molding material to minimizea positional error of the stator winding 51 in the stator 50 (see FIG.11). The rotating electrical machine 10 in this embodiment is designednot to have conductor-to-conductor members (e.g., teeth) between theconductor groups 81 arranged in the circumferential direction of thestator winding 51, thus leading to a concern about the positional erroror misalignment of the stator winding 51. The misalignment of theconductor of the stator winding 51 may be minimized by unifying thestator winding 51 and the stator core 52 in the mold. This eliminatesrisks of the distortion of magnetic flux arising from the misalignmentof the stator winding 51 and the electrical erosion in the bearings 21and 22 resulting from the distortion of the magnetic flux.

The unit base 61 serving as a housing to firmly fix the stator core 52is made of carbon fiber reinforced plastic (CFRP), thereby minimizingelectrical discharge to the unit base 61 as compared with when the unitbase 61 is made of aluminum, thereby avoiding the electrical erosion.

An additional erosion avoiding measure may be taken to make at least oneof the outer race 25 and the inner race 26 of each of the bearings 21and 22 using a ceramic material or alternatively to install aninsulating sleeve outside the outer race 25.

Other embodiments will be described below in terms of differencesbetween themselves and the first embodiment.

Second Embodiment

In this embodiment, the polar anisotropy structure of the magnet unit 42of the rotor 40 is changed and will be described below in detail.

The magnet unit 42 is, as clearly illustrated in FIGS. 22 and 23, madeusing a magnet array referred to as a Halbach array. Specifically, themagnet unit 42 is equipped with the first magnets 131 and the secondmagnets 132. The first magnets 131 have a magnetization direction (i.e.,an orientation of a magnetization vector thereof) oriented in the radialdirection of the magnet unit 42. The second magnets 132 have amagnetization direction (i.e., an orientation of the magnetizationvector thereof) oriented in the circumferential direction of the magnetunit 42. The first magnets 131 are arrayed at a given interval away fromeach other in the circumferential direction. Each of the second magnets132 is disposed between the first magnets 131 arranged adjacent eachother in the circumferential direction. The first magnets 131 and thesecond magnets 132 are each implemented by a rare-earth permanentmagnet, such as a neodymium magnet.

The first magnets 131 are arranged away from each other in thecircumferential direction so as to have N-poles and S-poles which arecreated in radially inner portions thereof and face the stator 50. TheN-poles and the S-poles are arranged alternately in the circumferentialdirection. The second magnets 132 are arranged to have N-poles andS-poles alternately located adjacent the first magnets 131 in thecircumferential direction. The cylinder 43 which surrounds the magnets131 and 132 may be formed as a soft magnetic core made of a softmagnetic material and which functions as a back core. The magnet unit 42in this embodiment are designed to have the easy axis of magnetizationoriented in the same way as in the first embodiment relative to thed-axis and the q-axis in the d-q axis coordinate system.

The magnetic members 133 each of which is made of a soft magneticmaterial are disposed radially outside the first magnets 131, in otherwords, close to the cylinder 43 of the magnet holder 41. Each of themagnetic members 133 may be made of magnetic steel sheet, soft iron, ora dust core material. Each of the magnetic members 133 has a lengthidentical with that of the first magnet 131 (especially, a length of anouter periphery of the first magnet 131) in the circumferentialdirection. An assembly made up of each of the first magnets 131 and acorresponding one of the magnetic members 133 has a thickness identicalwith that of the second magnet 132 in the radial direction. In otherwords, each of the first magnets 131 has the thickness smaller than thatof the second magnet 132 by that of the magnetic member 133 in theradial direction. The magnets 131 and 132 and the magnetic members 133are firmly secured to each other using, for example, adhesive agent. Inthe magnet unit 42, the radial outside of the first magnets 131 facesaway from the stator 50. The magnetic members 133 are located on theopposite side of the first magnets 131 to the stator 50 in the radialdirection (i.e., farther away from the stator 50).

Each of the magnetic members 133 has the key 134 in a convex shape whichis formed on the outer periphery thereof and protrudes radially outsidethe magnetic member 133, in other words, protrudes into the cylinder 43of the magnet holder 41. The cylinder 43 has the key grooves 135 whichare formed in an inner peripheral surface thereof in a concave shape andin which the keys 134 of the magnetic members 133 are fit. Theprotruding shape of the keys 134 is contoured to conform with therecessed shape of the key grooves 135. As many of the key grooves 135 asthe keys 134 of the magnetic members 133 are formed. The engagementbetween the keys 134 and the key grooves 135 serves to eliminatemisalignment or a positional deviation of the first magnets 131, thesecond magnets 132, and the magnet holder 41 in the circumferentialdirection (i.e. a rotational direction). The keys 134 and the keygrooves 135 (i.e., convexities and concavities) may be formed either onthe cylinders 43 of the magnet holder 41 or in the magnetic members 133,respectively. Specifically, the magnetic members 133 may have the keygrooves 135 in the outer periphery thereof, while the cylinder 43 of themagnet holder 41 may have the keys 134 formed on the inner peripherythereof.

The magnet unit 42 has the first magnets 131 and the second magnets 132alternately arranged to increase the magnetic flux density in the firstmagnets 131. This results in concentration of magnetic flux on onesurface of the magnet unit 42 to enhance the magnetic flux close to thestator 50.

The layout of the magnetic members 133 radially arranged outside thefirst magnets 131, in other words, farther away from the stator 50reduces partial magnetic saturation occurring radially outside the firstmagnets 131, thereby alleviating a risk of demagnetization in the firstmagnets 131 arising from the magnetic saturation. This results in anincrease in magnetic force produced by the magnet unit 42. In otherwords, the magnet unit 42 in this embodiment is viewed to have portionswhich are usually subjected to the demagnetization and replaced with themagnetic members 133.

FIGS. 24(a) and 24(b) are illustrations which demonstrate flows ofmagnetic flux in the magnet unit 42. FIG. 24(a) illustrates aconventional structure in which the magnet unit 42 is not equipped withthe magnetic members 133. FIG. 24(b) illustrates the structure in thisembodiment in which the magnet unit 42 is equipped with the magneticmembers 133. FIGS. 24(a) and 24(b) are linearly developed views of thecylinder 43 of the magnet holder 41 and the magnet unit 42. Lower sidesof FIGS. 24(a) and 24(b) are close to the stator 50, while upper sidesthereof are farther away from the stator 50.

In the structure shown in FIG. 24(a), a magnetic flux-acting surface ofeach of the first magnets 131 and a side surface of each of the secondmagnets 132 are placed in contact with the inner peripheral surface ofthe cylinder 43. A magnetic flux-acting surface of each of the secondmagnets 132 is placed in contact with the side surface of one of thefirst magnets 131. Such layout causes a combined magnetic flux to becreated in the cylinder 43. The combined magnetic flux is made up of amagnetic flux F1 which passes outside the second magnet 132 and thenenters the surface of the first magnets 131 contacting the cylinder 43and a magnetic flux which flows substantially parallel to the cylinder43 and attracts a magnetic flux F2 produced by the second magnet 132.This leads to a risk that the magnetic saturation may occur near thesurface of contact between the first magnet 131 and the second magnet132 in the cylinder 43

In the structure in FIG. 24(b) wherein each of the magnetic members 133is disposed between the magnetic flux-acting surface of the first magnet131 and the inner periphery of the cylinder 43 farther away from thestator 50, the magnetic flux is permitted to pass through the magneticmember 133. This minimizes the magnetic saturation in the cylinder 43and increases resistance against the demagnetization.

The structure in FIG. 24(b), unlike FIG. 24(a), functions to eliminatethe magnetic flux F2 facilitating the magnetic saturation. Thiseffectively enhances the permeance in the whole of the magnetic circuit,thereby ensuring the stability in properties of the magnetic circuitunder elevated temperature.

As compared with radial magnets used in conventional SPM rotors, thestructure in FIG. 24(b) has an increased length of the magnetic pathpassing through the magnet. This results in a rise in permeance of themagnet which enhances the magnetic force to increase the torque.Further, the magnetic flux concentrates on the center of the d-axis,thereby increasing the sine wave matching percentage. Particularly, theincrease in torque may be achieved effectively by shaping the waveformof the current to a sine or trapezoidal wave under PWM control or using120° excitation switching ICs

In a case where the stator core 52 is made of magnetic steel sheets, thethickness of the stator core 52 in the radial direction thereof ispreferably half or greater than half the thickness of the magnet unit 42in the radial direction. For instance, it is preferable that thethickness of the stator core 52 in the radial direction is greater thanhalf the thickness of the first magnets 131 arranged at the pole-to-polecenter in the magnet unit 42. It is also preferable that the thicknessof the stator core 52 in the radial direction is smaller than that ofthe magnet unit 42. In this case, a magnet magnetic flux isapproximately 1T, while the saturation magnetic flux density in thestator core 52 is 2T. The leakage of magnetic flux to inside the innerperiphery of the stator core 52 is avoided by selecting the thickness ofthe stator core 52 in the radial direction to be greater than half thatof the magnet unit 42.

Magnets arranged to have the Halbach structure or the polar anisotropicstructure usually have an arc-shaped magnetic path, so that the magneticflux may be increased in proportion to a thickness of ones of themagnets which handle a magnetic flux in the circumferential direction.In such a structure, the magnetic flux flowing through the stator core52 is thought of as not exceeding the magnetic flux flowing in thecircumferential direction. In other words, when the magnetic fluxproduced by the magnets is 1T, while ferrous metal whose saturationmagnetic flux density is 2T is used to make the stator core 52, a lightweight and compact electrical rotating machine may be produced byselecting the thickness of the stator core 52 to be greater than halfthat of the magnets. The demagnetizing field is usually exerted by thestator 50 on the magnetic field produced by the magnets, so that themagnetic flux produced by the magnets will be 0.9T or less. The magneticpermeability of the stator core may, therefore, be properly kept byselecting the thickness of the stator core to be half that of themagnets.

Modifications of the above structure will be described below.

First Modification

In the above embodiment, the outer peripheral surface of the stator core52 has a curved surface without any irregularities. The plurality ofconductor groups 81 are arranged at a given interval away from eachother on the outer peripheral surface of the stator core 52. This layoutmay be changed. For instance, the stator core 52 illustrated in FIG. 25is equipped with the circular ring-shaped yoke 141 and the protrusions142. The yoke 141 is located on the opposite side (i.e., a lower side,as viewed in the drawing) of the stator winding 51 to the rotor 40 inthe radial direction. Each of the protrusions 142 protrudes into a gapbetween a respective two of the straight sections 83 arranged adjacenteach other in the circumferential direction. The protrusions 142 arearranged at a given interval away from each other in the circumferentialdirection radially outside the yoke 141, i.e., close to the rotor 40.Each of the conductor groups 81 of the stator winding 51 engages theprotrusions 142 in the circumferential direction, in other words, theprotrusions 142 are used as positioners to position and array theconductor groups 81 in the circumferential direction. The protrusions142 correspond to conductor-to-conductor members.

A radial thickness of each of the protrusions 142 from the yoke 141, inother words, a distance W, as illustrated in FIG. 25, between the innersurface 320 of the straight sections 82 which is placed in contact withthe yoke 141 and the top of the protrusion 412 in the radial directionof the yoke 141 is selected to be smaller than half a radial thickness(as indicated by H1 in the drawing) of the straight sections 83 arrangedadjacent the yoke 141 in the radial direction. In other words,non-conductive members (i.e., the sealing members 57) preferably eachoccupy three-fourths of a dimension (i.e., thickness) T1 (i.e., twicethe thickness of the conductors 82, in other words, a minimum distancebetween the surface 320 of the conductor group 81 placed in contact withthe stator core 52 and the surface 330 of the conductor group 81 facingthe rotor 40) of the conductor groups (i.e., conductors) 81 in theradial direction of the stator winding 51 (i.e., the stator core 52).Such selection of the thickness of the protrusions 142 causes each ofthe protrusions 142 not to function as a tooth between the conductorgroups 81 (i.e., the straight sections 83) arranged adjacent each otherin the circumferential direction, so that there are no magnetic pathswhich would usually be formed by the teeth. The protrusions 142 need notnecessarily to be arranged between a respective circumferentiallyadjacent two of all the conductor groups 81, but however, a singleprotrusion 142 may be disposed at least only between two of theconductor groups 81 which are arranged adjacent each other in thecircumferential direction. For instance, the protrusions 142 may bedisposed away from each other in the circumferential direction at equalintervals each of which corresponds to a given number of the conductorgroups 81. Each of the protrusions 142 may be designed to have anyshape, such as a rectangular or arc-shape.

The straight sections 83 may alternatively be arranged in a single layeron the outer peripheral surface of the stator core 52. In a broad sense,the thickness of the protrusions 142 from the yoke 141 in the radialdirection may be smaller than half that of the straight sections 83 inthe radial direction.

If an imaginary circle whose center is located at the axial center ofthe rotating shaft 11 and which passes through the radial centers of thestraight sections 83 placed adjacent the yoke 141 in the radialdirection is defined, each of the protrusions 142 may be shaped toprotrude only within the imaginary circle, in other words, not toprotrude radially outside the imaginary circle toward the rotor 40.

The above structure in which the protrusions 142 have the limitedthickness in the radial direction and do not function as teeth in thegaps between the straight sections 83 arranged adjacent each other inthe circumferential direction enables the adjacent straight sections 83to be disposed closer to each other as compared with a case where teethare provided in the gaps between the straight sections 83. This enablesa sectional area of the conductor body 82 a to be increased, therebyreducing heat generated upon excitation of the stator winding 51. Theabsence of the teeth enables magnetic saturation to be eliminated toincrease the amount of electrical current delivered to the statorwinding 51. It is, however, possible to alleviate the adverse effectsarising from an increase in amount of heat generated by the increase inelectrical current delivered to the stator winding 51. The statorwinding 51, as described above, has the turns 84 which are shifted inthe radial direction and equipped with the interference avoidingportions with the adjacent turns 84, thereby enabling the turns 84 to bedisposed away from each other in the radial direction. This enhances theheat dissipation from the turns 84. The above structure is enabled tooptimize the heat dissipating ability of the stator 50.

The radial thickness of the protrusions 142 may not be restricted by thedimension H1 in FIG. 25 as long as the yoke 141 of the stator core 52and the magnet unit 42 (i.e., each of the magnets 91 and 92) of therotor 40 are arranged at a given distance away from each other.Specifically, the radial thickness of the protrusions 142 may be largerthan or equal to the dimension H1 in FIG. 25 as long as the yoke 141 andthe magnet unit 42 arranged 2 mm or more away from each other. Forinstance, in a case where the radial thickness of the straight section83 is larger than 2 mm, and each of the conductor groups 81 is made upof the two conductors 82 stacked in the radial direction, each of theprotrusions 142 may be shaped to occupy a region ranging to half thethickness of the straight section 83 not contacting the yoke 141, i.e.,the thickness of the conductor 82 located farther away from the yoke141. In this case, the above beneficial advantages will be obtained byincreasing the conductive sectional area of the conductor groups 81 aslong as the radial thickness of the protrusions 142 is at least H1×3/2.

The stator core 52 may be designed to have the structure illustrated inFIG. 26. FIG. 26 omits the sealing members 57, but the sealing members57 may be used. FIG. 26 illustrates the magnet unit 42 and the statorcore 52 as being arranged linearly for the sake of simplicity.

In the structure of FIG. 26, the stator 50 has the protrusions 142 asconductor-to-conductor members each of which is arranged between arespective two of the conductors 82 (i.e., the straight sections 83)located adjacent each other in the circumferential direction. The stator50 is equipped with the portions 350 each of which magnetically operatesalong with one of the magnetic poles (i.e., an N-pole or an S-pole) ofthe magnet unit 42 when the stator winding 51 is excited. The portions350 extend in the circumferential direction of the stator 50. If each ofthe portions 350 has a length Wn in the circumferential direction of thestator 50, the sum of widths of the protrusions 142 lying in a range ofthis length Wn (i.e., the total dimension of the protrusions 412 in thecircumferential direction of the stator 50 in the range of length Wn) isdefined as Wt, the saturation magnetic flux density of the protrusions412 is defined as Bs, a width of the magnet unit 42 equivalent to one ofthe magnetic poles of the magnet unit 42 in the circumferentialdirection of the magnet unit 42 is defined as Wm, and the remanent fluxdensity in the magnet unit 42 is defined as Br, the protrusions 142 aremade of a magnetic material meeting a relation of

Wt×Bs≤Wm×Br  (1)

The range Wn is defined to contain ones of the conductor groups 81 whichare arranged adjacent each other in the circumferential direction andwhich overlap in time of excitation thereof with each other. It isadvisable that a reference (i.e., a border) used in defining the rangeWn be set to the center of the gap 56 between the conductor groups 81.For instance, in the structure illustrated in FIG. 26, the plurality ofconductor groups 81 lying in the range Wn include the first, the second,the third, and the fourth conductor groups 81 where the first conductorgroup 81 is closest to the magnetic center of the N-pole. The range Wnis defined to include the total of those four conductor groups 81. Ends(i.e., outer limits) of the range Wn are defined to lie at the centersof the gaps 56.

In FIG. 26, the range Wn contains half of the protrusion 142 inside eachof the ends thereof. The total of the four protrusions 142 lie in therange Wn. If the width of each of the protrusions 142 (i.e., a dimensionof the protrusion 142 in the circumferential direction of the stator 50,in other words, an interval between the adjacent conductor groups 81) isdefined as A, the sum of widths Wt of the protrusions 142 lying in therange Wn meets a relation of Wt=½A+A+A+A+½A=4A.

Specifically, the three-phase windings of the stator winding 51 in thisembodiment are made in the form of distributed windings. In the statorwinding 51, the number of the protrusions 142 for each pole of themagnet unit 42, that is, the number of the gaps 56 each between theadjacent conductor groups 81 is selected to be “the number of phases×Q”where Q is the number of the conductors 82 for each phase which areplaced in contact with the stator core 52. In other words, in the casewhere the conductors 82 are stacked in the radial direction of the rotor40 to constitute each of the conductor groups 81, Q is the number ofinner ones of the conductors 82 of the conductor groups 81 for eachphase. In this case, when the three-phase windings of the stator winding51 are excited in a given sequence, the protrusions 142 for two of thethree-phases within each pole are magnetically excited. The totalcircumferential width Wt of the protrusions 142 excited upon excitationof the stator winding 51 within a range of each pole of the magnet unit42, therefore, meets a relation of “the number of the phasesexcited×Q×A=2×2×A where A is the width of each of the protrusions 142(i.e., the gap 56) in the circumferential direction.

The total width Wt is determined in the above way. Additionally, theprotrusions 142 of the stator core 52 are made of magnetic materialmeeting the above equation (1). The total width Wt is also viewed asbeing equivalent to a circumferential dimension of where the relativemagnetic permeability is expected to become greater than one within eachpole. The total width Wt may alternatively be determined as acircumferential width of the protrusions 142 in each pole with somemargin.

Specifically, since the number of the protrusions 142 for each pole ofthe magnet unit 42 is given by the number of phases×Q, the width of theprotrusions 412 in each pole (i.e., the total width Wt) may be given bythe number of phases×Q×A=3×2×A=6A.

The distributed winding, as referred to herein, means that there is apair of poles (i.e., the N-pole and the S-pole) of the stator winding 51for each pair of magnetic poles. The pair of poles of the stator winding51, as referred to herein, is made of the two straight sections 83 inwhich electrical current flows in opposite directions and the turn 84electrically connecting them together. Note that a short pitch windingor a full pitch winding may be viewed as an equivalent of thedistributed winding as long as it meets the above conditions.

Next, the case of a concentrated winding will be described below. Theconcentrated winding, as referred to herein, means that the width ofeach pair of magnetic poles is different from that of each pair of polesof the stator winding 51. An example of the concentrated windingincludes a structure in which there are three conductor groups 81 foreach pair of magnetic poles, in which there are three conductor groups81 for two pairs of magnetic poles, in which there are nine conductorgroups 81 for four pairs of magnetic poles, or in which there are nineconductor groups 81 for five pairs of magnetic poles.

In the case where the stator winding 51 is made in the form of theconcentrated winding, when the three-phase windings of the statorwinding 51 are excited in a given sequence, a portion of the statorwinding 51 for two phases is excited. This causes the protrusions 142for two phases to be magnetically excited. The circumferential width Wtof the protrusions 142 which is magnetically excited upon excitation ofthe stator winding in a range of each pole of the magnet unit 42 isgiven by Wt=A×2. The width Wt is determined in this way. The protrusions142 are made of magnetic material meeting the above equation (1). In theabove described case of the concentrated winding, the sum of widths ofthe protrusions 142 arranged in the circumferential direction of thestator 50 within a region surrounded by the conductor groups 81 for thesame phase is defined as A. The dimension Wm in the concentrated windingis given by [an entire circumference of a surface of the magnet unit 42facing the air gap]×[the number of phases]÷[the number of thedistributed conductor groups 81].

Usually, a neodymium magnet, a samarium-cobalt magnet, or a ferritemagnet whose value of BH is higher than or equal to 20[MGOe(kJ/m{circumflex over ( )}3)] has Bd=1.0T or more. Iron has Br=2.0T ormore. The protrusions 142 of the stator core 52 may, therefore, be madeof magnetic material meeting a relation of Wt<½×Wm for realizing ahigh-power motor.

In a case where each of the conductors 82 is, as described later,equipped with the outer coated layer 182, the conductors 82 may bearranged in the circumferential direction of the stator core with theouter coated layers 182 placed in contact with each other. In this case,the width Wt may be viewed to be zero or equivalent to thicknesses ofthe outer coated layers 182 of the conductors 82 contacting with eachother.

The structure illustrated in FIG. 25 or 26 is designed to haveconductor-to-conductor members (i.e., the protrusions 142) which are toosmall in size for the magnet-produced magnetic flux in the rotor 40. Therotor 40 is implemented by a surface permanent magnet rotor which has aflat surface and a low inductance, and does not have a salient pole interms of a magnetic resistance. Such a structure enables the inductanceof the stator 50 to be decreased, thereby reducing a risk of distortionof the magnetic flux caused by the switching time gap in the statorwinding 51, which minimizes the electrical erosion of the bearings 21and 22.

Second Modification

The stator 50 equipped with the conductor-to-conductor members made tomeet the above equation may be designed to have the following structure.In FIG. 27, the stator core 52 is equipped with the teeth 143 asconductor-to-conductor members which are formed in an outer peripheralportion (an upper portion, as viewed in the drawing) of the stator core52. The teeth 143 protrude from the yoke 141 and are arranged at a giveninterval away from each other in the circumferential direction of thestator core 52. Each of the teeth 143 has a thickness identical withthat of the conductor group 81 in the radial direction. The teeth 143have side surfaces placed in contact with the conductors 82 of theconductor groups 81. The teeth 143 may alternatively be located awayfrom the conductors 82 through gaps.

The teeth 143 are shaped to have a restricted width in thecircumferential direction. Specifically, each of the teeth 143 has astator tooth which is very thin for the volume of magnets.

Such a structure of the teeth 143 serves to achieve saturation by themagnet-produced magnetic flux at 1.8T or more to reduce the permeance,thereby decreasing the inductance.

If a surface area of a magnetic flux-acting surface of the magnet unit42 facing the stator 50 for each pole is defined as Sm, and the remanentflux density of the magnet unit 42 is defined as Br, the magnetic fluxin the magnet unit 42 will be Sm×Br. A surface area of each of the teeth143 facing the rotor 40 is defined as St. The number of the conductors83 for each phase is defined as m. When the teeth 143 for two phaseswithin a range of one pole are magnetically excited upon excitation ofthe stator winding 51, the magnetic flux in the stator 50 is expressedby St×m×2×Bs. The decrease in inductance may be achieved by selectingthe dimensions of the teeth 143 to meet a relation of

St×m×2×Bs<Sm×Br  (2).

In a case where the dimension of the magnet unit 42 is identical withthat of the teeth 143 in the axial direction, the above equation (2) maybe rewritten as an equation (3) of Wst×m×2×Bs<Wm×Br where Wm is thecircumferential width of the magnet unit 42 for each pole, and Wst isthe circumferential width of the teeth 143. For example, when Bs=2T,Br=1T, and m=2, the equation (3) will be Wst<Wm/8. In this case, thedecrease in inductance may be achieved by selecting the width Wst of theteeth 143 to be smaller than one-eighth (⅛) of the width Wm of themagnet unit 42 for one pole. When m is one, the width Wst of the teeth143 is preferably selected to be smaller than one-fourth (¼) of thewidth Wm of the magnet unit 42 for one pole.

“Wst×m×2” in the equation (3) corresponds to a circumferential width ofthe teeth 143 magnetically excited upon excitation of the stator winding51 in a range of one pole of the magnet unit 42.

The structure in FIG. 27 is, like in FIGS. 25 and 26, equipped with theconductor-to-conductor members (i.e., the teeth 143) which are verysmall in size for the magnet-produced magnetic flux in the rotor 40.Such a structure is capable of reducing the inductance of the stator 50to alleviate a risk of distortion of the magnetic flux arising from theswitching time gap in the stator winding 51, which minimizes theprobability of the electrical erosion of the bearings 21 and 22.

Third Modification

The above embodiment has the sealing members 57 which cover the statorwinding 51 and occupy a region including all of the conductor groups 81radially outside the stator core 52, in other words, lie in a regionwhere the thickness of the sealing members 57 is larger than that of theconductor groups 81 in the radial direction. This layout of the sealingmembers 57 may be changed. For instance, the sealing members 57 may be,as illustrated in FIG. 28, designed so that the conductors 82 protrudepartially outside the sealing members 57. Specifically, the sealingmembers 57 are arranged so that portions of the conductors 82 that areradially outermost portions of the conductor groups 81 are exposedoutside the sealing members 57 toward the stator 50. In this case, thethickness of the sealing members 57 in the radial direction may beidentical with or smaller than that of the conductor groups 81.

Fourth Modification

The stator 50 may be, as illustrated in FIG. 29, designed not to havethe sealing members 57 covering the conductor groups 81, i.e., thestator winding 51. In this case, a gap is created between the adjacentconductor groups 81 arranged in the circumferential direction without aconductor-to-conductor member therebetween. In other words, noconductor-to-conductor member is disposed between the conductor groups81 arranged in the circumferential direction. Air may be arranged in thegaps between the conductor groups 81. The air may be viewed as anon-magnetic member or an equivalent thereof whose Bs is zero (0).

Fifth Modification

The conductor-to-conductor members of the stator 50 may be made of anon-magnetic material other than resin. For instance, a non-metallicmaterial, such as SUS304 that is austenitic stainless steel.

Sixth Modification

This modification has a partially altered moulded structure for thestator winding 51. This modification and following modifications of themoulded structure for the stator winding 51 will refer only to partsdifferent from those already described with reference to FIGS. 10 and11.

The stator core 52 is, as clearly illustrated in FIG. 30, arrangedinside an inner periphery of the stator winding 51 (i.e., an oppositeside of the stator winding 51 than to the magnet unit 42). The statorcore 52 has a surface which faces the stator winding 51 and on whichconcavities and convexities are formed successively in a circumferentialdirection thereof. The concavities define the recesses 151 which arefilled with molding material. The molding material which forms thesealing members 57 enters the recesses 151. The molding material in therecesses 151 composes portions of the sealing members 57. Theconcavities and convexities may be formed by knurling. The concavitiesand convexities of the surface (e.g., knurled surface) of the statorcore 52 may alternatively be arranged successively adjacent each otheronly in the axial direction or both in the axial direction and in thecircumferential direction.

In this structure, molding materials are disposed intermittently betweenthe stator winding 51 and the stator core 52, thereby minimizingmisalignment of the molding materials with the stator core 52, in otherwords, holding the sealing members 57 which surround the conductorgroups 81 from moving. This eliminates a risk of misalignment of thestator winding 51.

When the concavities and convexities are arranged successively on thestator core 52 in the axial direction thereof, it minimizes misalignmentof the stator winding 51 in the axial direction. Alternatively, when theconcavities and convexities are arranged successively on the stator core52 in the circumferential direction thereof, it minimizes misalignmentof the stator winding 51 in the circumferential direction.

Seventh Modification

This modification has a partially altered moulded structure for thestator winding 51. In the structure in FIG. 31, the stator core 52 has aplurality of steel plates 52 a whose outer edges offset from each otherto have concavities and convexities on an outer peripheral surface ofthe stator core 52 which are arranged successively in the axialdirection. Molding materials are disposed in the recesses 152 defined bythe concavities and the convexities. The structure may have a stack ofsteel plates 52 a which are different in outer diameter from each other.

Eighth Modification

This modification has a partially altered moulded structure for thestator winding 51. In the structure illustrated in FIG. 32, each of thesteel plates 52 a has an end which faces the stator winding 51 and has across-section tapered in a thickness-wise direction. The tapered ends ofthe steel plates 52 a define successive recesses in which moldingmaterials are disposed. The stator core 52 made of a stack of steelplates has a concern about generation of eddy current in the steelplates 52 a when subjected to a strong magnetic field. Such a concernwill usually be strong on the ends of the steel plates 52 a close to thestator winding 51. The above structure in which the steel plates 52 ahave the tapered ends close to the stator winding 51, however, minimizesthe generation of eddy current.

Ninth Modification

This modification has a partially altered moulded structure for thestator winding 51. The structure illustrated in FIG. 33 has theinsulating layer 155 disposed between the stator winding 51 and thestator core 52. The insulating layer 155 is made from resin. Thestructure in this modification serves to block a flow of electricalcurrent arising from an electromagnetic field exerted by the statorwinding 51 on the stator core 52, thereby achieving a suitableelectrical erosion avoiding measure.

Tenth Modification

This modification has a partially altered moulded structure for thestator winding 51. The structure illustrated in FIG. 34 has the statorcore 52 in which the resin-injecting holes 156 are formed. Theresin-injecting holes 156 extend in the axial direction and are eachfilled with a molding material (i.e., resin). The resin-injecting holes156 are through-holes extending from one end to the other end of thestator core 52 in the axial direction and arranged at a given intervalaway from each other in the circumferential direction. This keeps moldedmembers (i.e., the sealing members 57) arranged at fixed locations inthe circumferential and axial directions, thereby improving thestructure to minimize misalignment of the stator winding 51.

The resin-injecting holes 156 of the stator core 52 are located awayfrom the stator winding 51 in the radius direction, thereby reducingadverse effects on the magnetic circuits to ensure the stability inoperation of the rotating electrical machine 10.

In the stator core 52 made of a stack of steel plates, burrs of thesteel plates usually make irregularities on peripheral surfaces of theresin-injecting holes 156. The molding material enters theirregularities, which function as anchors to hold the stator winding 51from being misaligned. Each of the resin-injecting holes 156 mayalternatively be implemented by a hole not extending through the statorcore 52 in the axial direction.

In the structure illustrated in FIG. 34, the stator winding 51 iscovered with or embedded in a molding material except portions extendingin the axial direction or the radial direction. In other words, portionsof the stator winding 51 are exposed outside the molding material. Morespecifically, the coil ends 54 and 55 (i.e., axially-opposed ends) ofthe stator winding 51 are partially exposed outside the moldingmaterial. The stator winding 51 may alternatively be designed only tohave portions extending in the radial direction outside the moldingmaterial (see FIG. 28).

The stator winding 51, therefore, has the above described advantage thatthe stator winding 51 is held by the mold from being misaligned, and theportions of the stator winding 51 which are not embedded in the moldserve to enhance a cooling effect. It is, therefore, possible to achieveboth the misalignment reducing effect and the cooling effect. Therotating electrical machine 10 may have a structure to cool a motorhousing using cooling wind produced by rotation of the rotating shaft 11and the rotor 40 or cool the stator 50 using a liquid cooling medium. Inthis case, the stator winding 51 has portions exposed outside themolding material (i.e., the sealing members 57), so that the exposedportions are cooled by air or cooling medium, thereby enhancing thecooled ability of the stator winding 51.

Eleventh Modification

This modification has a partially altered moulded structure for thestator winding 51. In the structure illustrated in FIG. 35, theinsulating layer 157 made from resin is disposed between the stator core52 and the unit base 61. This structure serve to block a flow ofelectrical current arising from an electromagnetic field exerted by thestator core 51 on the unit base 61, thereby achieving a suitableelectrical erosion avoiding measure.

Twelfth Modification

In this modification, the rotor 40 serving as a magnetic field-producingunit has a skew structure. Specifically, the rotor 40 has the magnetunit 42 designed to have the skew structure in which magnetic poleswhich are arranged in the axial direction of the rotating shaft 11 areoffset from each other in the circumferential direction of the rotor 40.Particularly, the magnetic poles of the magnet unit 42 have respectivemagnetic pole center lines each of which extends in the axial directionand which is skewed by either a first amount in a first circumferentialdirection of the rotor 40 or a second amount in a second circumferentialdirection opposite the first circumferential direction of the rotor 40.The first and second amounts (which will also be referred to as skewamounts) are identical with each other.

The skew structure of the rotor 40 will be described below in detailwith reference to FIGS. 36(a) and 36(b). FIGS. 36(a) and 36(b) are frontviews schematically illustrating locations of the magnets 91 havinggiven magnetic poles. The skew structure in each of FIGS. 36(a) and36(b) has axially-opposed end portions and a middle portion between theend portions. Each of the end portions and the middle portion aredifferent in skew orientation from each other in the form of a so-calledV-shaped skew.

The structure in FIG. 36(a) is a skew structure in which locations ofthe magnets 91 in the circumferential direction are misaligned to bestepwise in the axial direction. The structure has two first portions B1that are axially-opposed ends and a second portion B2 intermediatebetween the first portions B1. The first portions B1 are different incircumferential location from the second portion B2. In each of thefirst portions B1, the circumferential location of the magnet 91 isoffset leftward, as viewed in the drawing, from the magnetic pole centerline LA. In the second portion B2, the circumferential location of themagnet 91 is offset rightward, as viewed in the drawing, from themagnetic pole center line LA. The skew amount L1 of each of the firstportions B1 from the magnetic pole center line LA in the firstcircumferential direction is identical with the skew amount L2 of thesecond portions B2 from the magnetic pole center line LA in the secondcircumferential direction opposite the first circumferential direction.The first portions B1 have a length in the axial direction which isidentical with that of the second portion B2. Each of the skew amountsL1 and L2 is given by a distance between the magnetic pole center lineLA and the center line of the magnet 91 in the circumferentialdirection. Each of the first portions B1 has a length in the axialdirection which is half that of the second portion B2.

The structure in FIG. 36(b) is a skew structure in which acircumferential location of each of the magnets 91 is changed obliquelyin the axial direction. The structure has a first portion B11 given byone of axially opposed ends thereof and a second portion B12 given bythe other end. Directions in which the first portion B11 and the secondportion B12 are inclined are oriented to be different from each otherrelative to the axial direction. The first portion B11 and the secondportion B12 are symmetric with respect to an axial boundary line of thefirst and second portions B11 and B12. Each of the first and secondportions B11 and B12 has a magnet unit center line LB extendingobliquely in a skew direction. The magnet unit center lines LB of thefirst and second portions B11 and B12 intersect with the magnetic polecenter line LA at the axial center positions P1 and P2, respectively.The angles θ1 and θ2 at which the magnets 91 are inclined in the firstportion B11 and the second portion B12 are identical with each other.

The structure in which the rotor 40 is skewed is expected to offer aneffect of reducing torque ripple and a resulting effect of improvingnoise-reduction, but has a concern about electrical erosion of thebearings 21 and 22 arising from unbalance of magnetic fluxes in theaxial direction. The above structure is designed to have the equal firstand second skew amounts from the magnetic pole center line LA of eachmagnetic pole extending in the axial direction in the magnet unit 42,thereby cancelling electrical currents flowing in the axial direction.This minimizes a risk of electrical erosion of the bearings 21 and 22.

Thirteenth Modification

This modification has the stator 50 serving as an armature which isdesigned to be of a skew structure. Specifically, the rotor 50 has theskew structure in which conductor locations of the stator winding 51 foreach phase in the axial direction of the rotating shaft 11 are offset inthe circumferential direction. A first amount by which each of the phasewindings of the stator winding 51 is skewed in a first circumferentialdirection from an energized phase center line extending in the axialdirection is selected to be identical with a second amount by which eachof the phase windings of the stator winding 51 for each phase is skewedin a second circumferential direction oppose the first circumferentialdirection from the energized phase center line.

The skew structure of the stator 50 will be described below in detailwith reference to FIGS. 37(a) and 37(b). FIGS. 37(a) and 37(b) are frontviews schematically illustrating layout of the conductors 82 for a givenphase. The stator winding 51 is required to have the conductors 82connected continuously together. The skew structure is, therefore,employed in which conductor locations of the stator winding 51 for eachphase are changed obliquely in the circumferential direction.

The structure illustrated in FIG. 37(a) is designed as a skew structurein which each of the conductors 82 has a magnet-facing portion (i.e., acoil side) which is bent or turned back. The conductor 82 includes afirst section C1 and a second section C2 which are different in inclinedorientation of the conductor 82 from each other in the axial direction.The first and second sections C1 and C2 are vertically symmetric witheach other with respect to the axially center point of the stator 50.The first and second sections C1 and C2 have centers P11 and P12 ofaxial lengths thereof which intersect with the energized phase centerline LC extending in the axial direction.

The structure illustrated in FIG. 37(b) is designed as a skew structurein which each of the conductors 82 has a magnet-facing portion (i.e., acoil side) which is not turned back, in other words, the magnet-facingportion of the conductor 82 extend obliquely straight. The conductor 82,as indicated by a solid line in FIG. 37(b), is a conductor of an outerone of two layers of the stator winding 51 which are arranged adjacenteach other in the radial direction. The conductor 82, as indicated by abroken line in FIG. 37(b), is a conductor of an inner one of the twolayers. The conductor 82 of the outer layer is skewed in a directionopposite that in which the conductor 82 of the inner layer is skewed.The conductor 82 of each of the outer and inner layers has an axialcenter P13 intersecting with the energized phase center line LC.

The structure in which the stator 50 is skewed is expected to offer aneffect of reducing torque ripple, but has a concern about electricalerosion of the bearings 21 and 22 arising from promoted unbalance ofmagnetic fluxes in the axial direction. The above structure is designedto have the first and second skew amounts by which the phase windings ofthe stator winding 51 are skewed in the first and second circumferentialdirections from the energized phase center line LC extending in theaxial direction and which are equal to each other, thereby cancellingelectrical currents flowing in the axial direction. This minimizes arisk of electrical erosion of the bearings 21 and 22.

Both the rotor 40 and the stator 50 may be designed to have the skewstructure. In other words, the structures in FIGS. 36(a) and 36(b) andFIGS. 37(a) and 37(b) may be combined.

The rotating electrical machine 10 described in the first embodiment hasthe rotor 40 and the stator 50 which are both designed as a non-skewstructure which does not offer an effect of reduction in the torqueripple which usually results from the skew, but has an advantage thatthe imbalance of magnetic fluxes arising from the skew does not occur.

Fourteenth Modification

The stator 50 may be designed not to have the stator core 52.Specifically, the stator 50 is made of the stator winding 51 shown inFIG. 12. The stator winding 51 of the stator 50 may be covered with asealing member. The stator 50 may alternatively be designed to have anannular winding retainer made from non-magnetic material such assynthetic resin instead of the stator core 52 made from soft magneticmaterial.

Fifteenth Modification

The structure in the first embodiment uses the magnets 91 and 92arranged in the circumferential direction to constitute the magnet unit42 of the rotor 40. The magnet unit 42 may be made using a circularring-shaped permanent magnet. For instance, the arc-shaped or annularmagnet 95 is, as illustrated in FIG. 38, secured to a radially innerperiphery of the cylinder 43 of the magnet holder 41. The annular magnet95 is equipped with a plurality of different magnetic poles whosepolarities are arranged alternately in the circumferential direction ofthe annular magnet 95. The magnet 95 lies integrally both on the d-axisand the q-axis. The annular magnet 95 has a magnetic orientationdirected in the radial direction on the d-axis of each magnetic pole anda magnetic orientation directed in the circumferential direction on theq-axis between the magnetic poles, thereby creating arc-shaped magneticpaths.

The annular magnet 95 may be magnetically oriented to create thearc-shaped magnet-produced magnetic path in which the easy axis ofmagnetization is directed parallel or near parallel to the d-axis in theregion close to the d-axis and also directed perpendicular or nearperpendicular to the q-axis in the region close to the q-axis.

Sixteenth Modification

This modification is different in operation of the controller 110 fromthe above embodiment or modifications. Only differences from those inthe first embodiment will be described below.

The operations of the operation signal generators 116 and 126illustrated in FIG. 20 and the operation signal generators 130 a and 130b illustrated in FIG. 21 will first be discussed below using FIG. 39.The operations executed by the operation signal generators 116, 126, 130a, and 130 b are basically identical with each other. Only the operationof the operation signal generator 116 will, therefore, be describedbelow for the sake of simplicity.

The operation signal generator 116 includes the carrier generator 116 a,the U-phase comparator 116 bU, the V-phase comparator 116 bV, and theW-phase comparator 116 bW. The carrier generator 116 a produces andoutputs the carrier signal SigC in the form of a triangle wave signal.

The U-, V-, and W-phase comparators 116 bU, 116 bV, and 116 bW receivethe carrier signal SigC outputted by the carrier generator 116 a and theU-, V-, and W-phase command voltages produced by the three-phaseconverter 115. The U-, V-, and W-phase command voltages are produced,for example, in the form of a sine wave and outputted 120° out ofelectrical phase with each other.

The U-, V-, and W-phase comparators 116 bU, 116 bV, and 116 bW comparethe U-, V-, and W-phase command voltages with the carrier signal SigC toproduce operation signals for the switches Sp and Sn of the upper andlower arms in the first inverter 101 for the U-, V-, and W-phasewindings under PWM (Pulse Width Modulation) control. Specifically, theoperation signal generator 116 works to produce operation signals forthe switches Sp and Sn of the upper and lower arms for the U-, V-, andW-phase windings under the PWM control based on comparison of levels ofsignals derived by normalizing the U-, V-, and W-phase command voltagesusing the power supply voltage with a level of the carrier signal SigC.The driver 117 is responsive to the operation signals outputted by theoperation signal generator 116 to turn on or off the switches Sp and Snin the first inverter 101 for the U-, V-, and W-phase windings.

The controller 110 alters the carrier frequency fc of the carrier signalSigC, i.e., a switching frequency for each of the switches Sp and Sn.The carrier frequency fc is altered to be higher in a low torque rangeor a high-speed range in the rotating electrical machine 10 andalternatively lower in a high torque range in the rotating electricalmachine 10. This altering is achieved in order to minimize adeterioration in ease of control of electrical current flowing througheach of the U-, V-, and W-phase windings.

In brief, the core-less structure of the stator 50 serves to reduce theinductance in the stator 50. The reduction in inductance usually resultsin a decrease in electrical time constant in the rotating electricalmachine 10. This leads to a risk that a ripple of current flowingthrough each of the phase windings may be increased, thereby resultingin the deterioration in ease of control of the current flowing throughthe phase winding, which causes control divergence. The adverse effectsof the above deterioration of the ease of control usually become higherwhen the current (e.g., an effective value of the current) flowingthrough the winding lies in a low current region than when the currentlies in a high current range. In order to alleviate such a problem, thecontroller 110 in this embodiment is designed to alter the carrierfrequency fc.

How to alter the carrier frequency fc will be described below withreference to FIG. 40. This operation of the operation signal generator116 is executed by the controller 110 cyclically at a given interval.

First, in step S10, it is determined whether electrical current flowingthrough each of the three-phase windings 51 a lies in the low currentrange. This determination is made to determine whether torque nowproduced by the rotating electrical machine 10 lies in the low torquerange. Such a determination may be achieved according to the firstmethod or the second method, as discussed below.

First Method

The estimated torque value of the rotating electrical machine 10 iscalculated using the d-axis current and the q-axis current converted bythe d-q converter 112. If the estimated torque value is determined to belower than a torque threshold value, it is concluded that the currentflowing through the winding 51 a lies in the low current range.Alternatively, if the estimated torque value is determined to be higherthan or equal to the torque threshold value, it is concluded that thecurrent lies in the high current range. The torque threshold value isselected to be half, for example, the degree of starting torque (alsocalled locked rotor torque) in the rotating electrical machine 10.

Second Method

If an angle of rotation of the rotor 40 measured by an angle sensor isdetermined to be higher than or equal to a speed threshold value, it isdetermined that the current flowing through the winding 51 a lies in thelow current range, that is, in the high speed range. The speed thresholdvalue may be selected to be a rotational speed of the rotatingelectrical machine 10 when a maximum torque produced by the rotatingelectrical machine 10 is equal to the torque threshold value.

If a NO answer is obtained in step S10, meaning that the current lies inthe high current range, then the routine proceeds to step S11 whereinthe carrier frequency fc is set to the first frequency fL.

Alternatively, if a YES answer is obtained in step S10, then the routineproceeds to step S12 wherein the carrier frequency fc is set to thesecond frequency fH that is higher than the first frequency fL.

As apparent from the above discussion, the carrier frequency fc when thecurrent flowing through each of the three-phase windings lies in the lowcurrent range is selected to be higher than that when the current liesin the high current range. The switching frequency for the switches Spand Sn is, therefore, increased in the low current range, therebyminimizing a rise in current ripple to ensure the stability incontrolling the current.

When the current flowing through each of the three-phase windings liesin the high current range, the carrier frequency fc is selected to belower than that when the current lies in the low current range. Thecurrent flowing through the winding in the high current range usuallyhas an amplitude larger than that when the current lies in the lowcurrent range, so that the rise in current ripple arising from thereduction in inductance has a low impact on the ease of control of thecurrent. It is, therefore, possible to set the carrier frequency fc inthe high current range to be lower than that in the low current range,thereby reducing a switching loss in the inverters 101 and 102.

This modification is capable of realizing the following modes.

If a YES answer is obtained in step S10 in FIG. 40 when the carrierfrequency fc is set to the first frequency fL, the carrier frequency fcmay be changed gradually from the first frequency fL to the secondfrequency fH.

Alternatively, if a NO answer is obtained in step S10 when the carrierfrequency fc is set to the second frequency fH, the carrier frequency fcmay be changed gradually from the second frequency fH to the firstfrequency fL.

The operation signals for the switches may alternatively be producedusing SVM (Space Vector Modulation) instead of the PWM. The abovealtering of the switching frequency may also be made.

Seventeenth Modification

In each of the embodiments, two pairs of conductors making up theconductor groups 81 for each phase are, as illustrated in FIG. 41(a),arranged parallel to each other. FIG. 41(a) is a view which illustratesan electrical connection of the first and second conductors 88 a and 88b that are the two pairs of conductors. The first and second conductors88 a and 88 b may alternatively be, as illustrated in FIG. 41(b),connected in series with each other instead of the connection in FIG.41(a).

Three or more pairs of conductors may be stacked in the form of multiplelayers. FIG. 42 illustrates four pairs of conductors: the first tofourth conductors 88 a to 88 d which are stacked. The first conductor 88a, the second conductor 88 b, the third conductor 88 c, and the fourthconductor 88 d are arranged in this order from the stator core 52 in theradial direction.

The third and fourth conductors 88 c and 88 d are, as illustrated inFIG. 44(c), connected in parallel to each other. The first conductor 88a is connected to one of joints of the third and fourth conductors 88 cand 88 d. The second conductor 88 b is connected to the other joint ofthe third and fourth conductors 88 c and 88 d. The parallel connectionof conductors usually results in a decrease in current density of thoseconductors, thereby minimizing thermal energy produced upon energizationof the conductors. Accordingly, in the structure in which a cylindricalstator winding is installed in a housing (i.e., the unit base 61) withthe coolant path 74 formed therein, the first and second conductors 88 aand 88 b which are connected in non-parallel to each other are arrangedclose to the stator core 52 placed in contact with the unit base 61,while the third and fourth conductors 88 c and 88 d which are connectedin parallel to each other are disposed farther away from the stator core52. This layout equalizes the cooling ability of the conductors 88 a to88 d stacked in the form of multiple layers.

The conductor group 81 including the first to fourth conductors 88 a to88 d may have a thickness in the radial direction which is smaller thana circumferential width of the conductor groups 81 for one phase withina region of one pole.

Eighteenth Modification

The rotor 40 of the rotating electrical machine 10 may be designed asdescribed below. In FIG. 43(a), the cylinder 43 of the magnet holder 41is equipped with the back core 48 made of a stack of magnetic steelplates. The magnet unit 42 is arranged radially inside the back core 48.More specifically, the back core 48 has the housing recess 48 a which isdefined inside an inner periphery thereof and in which the magnet unit42 is stored. The magnet unit 42 is disposed fully or partially insidethe housing recess 48 a with axially opposed end surfaces thereof placedin contact with the back core 48. This structure minimizes leakage ofmagnetic flux from the axially opposed ends of the magnet unit 42 andalso greatly enhances a resistance to demagnetization thereof, whichresults from a reduction in magnetic resistance of iron.

Nineteenth Modification

The rotating electrical machine 10 may alternatively be designed to havean inner rotor structure (i.e., an inward rotating structure). In thiscase, the stator 50 may be mounted, for example, on a radial outsidewithin the housing 30, while the rotor 40 may be disposed on a radialinside within the housing 30. The inverter unit 60 may be mounted one orboth axial sides of the stator 50 or the rotor 40. FIG. 44 is atransverse sectional view of the rotor 40 and the stator 50. FIG. 45 isan enlarged view which partially illustrates the rotor 40 and the stator50 in FIG. 44.

The inner rotor structure in FIGS. 44 and 45 is substantially identicalwith the outer rotor structure in FIGS. 8 and 9 except for the layout ofthe rotor 40 and the stator 50 in the radial direction. In brief, thestator 50 is equipped with the stator winding 51 having the flattenedconductor structure and the stator core 52 with no teeth. The statorwinding 51 is installed radially inside the stator core 52. The statorcore 52, like the outer rotor structure, has any of the followingstructures.

(A) The stator 50 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. As the conductor-to-conductor members, magnetic material isused which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is the saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris the remanent flux density in the magnet unit.(B) The stator 50 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. The conductor-to-conductor members are each made of anon-magnetic material.(C) The stator 50 has no conductor-to-conductor member disposed betweenthe conductor portions in the circumferential direction.

The same is true of the magnets 91 and 92 of the magnet unit 42.Specifically, the magnet unit 42 is made up of the magnets 91 and 92each of which is magnetically oriented to have the easy axis ofmagnetization which is directed near the d-axis to be more parallel tothe d-axis than that near the q-axis which is defined on the boundary ofthe magnetic poles. The details of the magnetization direction in eachof the magnets 91 and 92 are the same as described above. The magnetunit 42 may be the annular magnet 95 (see FIG. 38).

FIG. 46 is a longitudinal sectional view of the rotating electricalmachine 10 designed to have the inner rotor structure. FIG. 46corresponds to FIG. 2. Differences from the structure in FIG. 2 will bedescribed below in brief. In FIG. 46, the annular stator 50 is retainedinside the housing 30. The rotor 40 is disposed inside the stator 50with an air gap therebetween to be rotatable. The bearings 21 and 22are, like in FIG. 2, offset from the axial center of the rotor 40 to oneof axially-opposed ends of the rotor 40, so that the rotor 40 isretained in the cantilever form. The inverter 60 is mounted inside themagnet holder 41 of the rotor 40.

FIG. 47 illustrates the inner rotor structure of the rotating electricalmachine 10 which is different from that described above. The housing 30has the rotating shaft 11 retained by the bearings 21 and 22 to berotatable. The rotor 40 is secured to the rotating shaft 11. Like thestructure in FIG. 2, each of the bearings 21 and 22 is offset from theaxial center of the rotor 40 in the axial direction of the rotor 40. Therotor 40 is equipped with the magnet holder 41 and the magnet unit 42.

The rotating electrical machine 10 in FIG. 47 is different from that inFIG. 46 in that the inverter unit 60 is not located radially inside therotor 40. The magnet holder 41 is joined to the rotating shaft 11radially inside the magnet unit 42. The stator 50 is equipped with thestator winding 51 and the stator core 52 and secured to the housing 30.

Twentieth Modification

This modification has the rotating shaft 11 equipped with an insulatinglayer which is disposed on an outer periphery thereof and has an outerperiphery to which a rotor is secured. Specifically, the rotating shaft11, as clearly illustrated in FIG. 48(a), has the insulating layer 161wrapped fully about the whole of an outer periphery thereof. The rotor40 is arranged outside the insulating layer 161. The insulating layer161 is made from, for example, a resinous material. The magnet holder 41of the rotor 40 is attached to the rotating shaft 11 through theinsulating layer 161 disposed between itself and the rotating shaft 11.The rotating shaft 11 may alternatively be, as illustrated in FIG.48(b), designed to have a recess which is formed in the outer peripherythereof and in which the insulating layer 161 is disposed.

The above structure serves to block an axial current flowing in therotating shaft 11 using the insulating layer 161, thereby minimizing arisk of electrical erosion.

Twenty-First Modification

The inner rotor structure of a rotating electrical machine which isdifferent from that described above will be discussed below. FIG. 49 isan exploded perspective view of the rotating electrical machine 200.FIG. 50 is a sectional side view of the rotating electrical machine 200.In the following discussion, a vertical direction is based on theorientation of the rotating electrical machine 200 in FIGS. 39 and 50.

The rotating electrical machine 200, as illustrated in FIGS. 49 and 50,includes the stator 203 and the rotor 204. The stator 203 is equippedwith the annular stator core 201 and the multi-phase stator winding 202.The rotor 204 is disposed inside the stator core 201 to be rotatable.The stator 203 works as an armature. The rotor 204 works as a fieldmagnet. The stator core 201 is made of a stack of silicon steel plates.The stator winding 202 is installed in the stator core 201. Although notillustrated, the rotor 204 is equipped with a rotor core and a pluralityof permanent magnet arranged in the form of a magnet unit. The rotorcore has formed therein a plurality of holes which are arranged at equalintervals away from each other in the circumferential direction of therotor core. The permanent magnets which are magnetized to havemagnetization directions changed alternately in adjacent magnetic polesare disposed in the holes of the rotor core. The permanent magnets ofthe magnet unit may be designed, like in FIG. 23, to have a Halbacharray structure or a similar structure. The permanent magnets of themagnet unit may alternatively be made of anisotropic magnets, asdescribed with reference to FIG. 9 or 30, in which the magneticorientation (i.e., the magnetization direction) extends in an arc-shapebetween the d-axis which is defined on the magnetic center and theq-axis which is defined on the boundary of the magnetic poles.

The stator 203 may be made to have one of the following structures.

(A) The stator 203 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. As the conductor-to-conductor members, magnetic material isused which meets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is the saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris the remanent flux density in the magnet unit.(B) The stator 203 has the conductor-to-conductor members each of whichis disposed between the conductor portions in the circumferentialdirection. The conductor-to-conductor members are each made of anon-magnetic material.(C) The stator 203 has no conductor-to-conductor member disposed betweenthe conductor portions in the circumferential direction.

The rotor 204 has the magnet unit which is made up of a plurality ofmagnets each of which is magnetically oriented to have the easy axis ofmagnetization which is directed near the d-axis to be more parallel tothe d-axis than that near the q-axis which is defined on the boundary ofthe magnetic poles.

The annular inverter case 211 is disposed on one end side of an axis ofthe rotating electrical machine 200. The inverter case 211 has a lowersurface placed in contact with an upper surface of the stator core 201.The inverter case 211 has disposed therein a plurality of power modules212 constituting an inverter circuit, the smoothing capacitors 213working to reduce a variation in voltage or current (i.e., a ripple)resulting from switching operations of semiconductor switches, thecontrol board 214 equipped with a controller, the current sensor 215working to measure a phase current, and the resolver stator 216 servingas a rotational speed sensor for the rotor 204. The power modules 212are equipped with IGBTs serving as semiconductor switches and diodes.

The inverter case 211 has the power connector 217 which is disposed on acircumferential edge thereof for connection with a dc circuit for abattery mounted in a vehicle. The inverter case 211 also has the signalconnector 218 which is disposed on the circumferential edge thereof forachieving transmission of signals between the rotating electricalmachine 200 and a controller installed in the vehicle. The inverter case211 is covered with the top cover 219. The dc power produced by thebattery installed in the vehicle is inputted into the power connector217, converted by the switches of the power modules 212 to analternating current, and then delivered to phase windings of the statorwinding 202.

The bearing unit 221 and the annular rear case 222 are disposed on theopposite end side of the axis of the stator core to the inverter case211. The bearing unit 221 retains a rotation shaft of the rotor 204 tobe rotatable. The rear case 222 has the bearing unit 221 disposedtherein. The bearing unit 221 is equipped with, for example, twobearings and offset from the center of the length of the rotor 204toward one of the ends of the length of the rotor 204. The bearing unit221 may alternatively be engineered to have a plurality of bearingsdisposed on both end sides of the stator core 201 opposed to each otherin the axial direction, so that the bearings retain both the ends of therotation shaft. The rear case 222 is fastened to a gear case or atransmission of the vehicle using bolts, thereby securing the rotatingelectrical machine 200 to the vehicle.

The inverter case 211 has formed therein the cooling flow path 211 athrough which cooling medium flows. The cooling flow path 211 a isdefined by closing an annular recess formed in a lower surface of theinverter case 211 by an upper surface of the stator core 201. Thecooling flow path 211 a surrounds a coil end of the stator winding 202.The cooling flow path 211 a has the module cases 212 a of the powermodules 212 disposed therein. Similarly, the rear case 222 has formedtherein the cooling flow path 222 a which surrounds a coil end of thestator winding 202. The cooling flow path 222 a is defined by closing anannular recess formed in an upper surface of the rear case 222 by alower surface of the stator core 201.

Twenty-Second Modification

The above discussion has referred to the revolving-field type ofrotating electrical machines, but a revolving armature type of rotatingelectrical machine may be embodied. FIG. 51 illustrates the revolvingarmature type of rotating electrical machine 230.

The rotating electrical machine 230 in FIG. 51 has the bearing 232retained by the housings 231 a and 231 b. The bearing 232 retains therotating shaft 233 to be rotatable. The bearing 232 is made of, forexample, an oil-impregnated bearing in which a porous metal isimpregnated with oil. The rotating shaft 233 has secured thereto therotor 234 which works as an armature. The rotor 234 includes the rotorcore 235 and the multi-phase rotor winding 236 secured to an outerperiphery of the rotor core 235. The rotor core 235 of the rotor 234 isdesigned to have the slot-less structure. The multi-phase rotor winding236 has the flattened conductor structure as described above. In otherwords, the multi-phase rotor winding 236 is shaped to have an area foreach phase which has a dimension in the circumferential direction whichis larger than that in the radial direction.

The stator 237 is disposed radially outside the rotor 234. The stator237 works as a field magnet. The stator 237 includes the stator core 238and the magnet unit 239. The stator core 238 is secured to the housing231 a. The magnet unit 239 is attached to an inner periphery of thestator core 238. The magnet unit 239 is made up of a plurality ofmagnets arranged to have magnetic poles alternately arrayed in thecircumferential direction. Like the magnet unit 42 described above, themagnet unit 239 is magnetically oriented to have the easy axis ofmagnetization which is directed near the d-axis to be more parallel tothe d-axis than that near the q-axis that is defined on a boundarybetween the magnetic poles. The magnet unit 239 is equipped withmagnetically oriented sintered neodymium magnets whose intrinsiccoercive force is 400 [kA/m] or more and whose remanent flux density is1.0 [T] or more.

The rotating electrical machine 230 in this embodiment is engineered asa two-pole three-coil brush coreless motor. The multi-phase rotorwinding 236 is made of three coils. The magnet unit 239 is designed tohave two poles. A ratio of the number of poles and the number of coilsin typical brush motors is 2:3, 4:10, or 4:21 depending upon intendeduse.

The rotating shaft 233 has the commutator 241 secured thereto. Aplurality of brushes 242 are arranged radially outside the commutator241. The commutator 241 is electrically connected to the multi-phaserotor winding 236 through the conductors 234 embedded in the rotatingshaft 233. The commutator 241, the brushes 242, and the conductors 243are used to deliver dc current to the multi-phase rotor winding 236. Thecommutator 241 is made up of a plurality of sections arrayed in acircumferential direction thereof depending upon the number of phases ofthe multi-phase rotor winding 236. The brushes 242 may be connected to adc power supply, such as a storage battery, using electrical wires orusing a terminal block.

The rotating shaft 233 has the resinous washer 244 disposed between thebearing 232 and the commutator 241. The resinous washer 244 serves as asealing member to minimize leakage of oil seeping out of the bearing232, implemented by an oil-impregnated bearing, to the commutator 241.

Twenty-Third Modification

Each of the conductors 82 of the stator winding 51 of the rotatingelectrical machine 10 may be designed to have a stack of a plurality ofinsulating coatings or layers laid on each other. For instance, each ofthe conductors 82 may be made by covering a bundle of a plurality ofinsulating layer-coated conductors (i.e., wires) with an insulatinglayer, so that the insulating layer (i.e., an inner insulating layer) ofeach of the conductors 82 is covered with the insulating layer (i.e., anouter insulating layer) of the bundle. The outer insulating layer ispreferably designed to have an insulating ability greater than that ofthe inner insulating layer. Specifically, the thickness of the outerinsulating layer is selected to be larger than that of the innerinsulating layer. For instance, the outer insulating layer has athickness of 100 μm, while the inner insulating layer has a thickness of40 μm. Alternatively, the outer insulating layer may have a permittivitylower than that of the inner insulating layer. Each of the conductors 82may have any of the above structure. Each wire is preferably made of acollection of conductive members or fibers.

As apparent from the above discussion, the rotating electrical machine10 becomes useful in a high-voltage system of a vehicle by increasingthe insulation ability of the outermost layer of the conductor 82. Theabove structure enables the rotating electrical machine 10 to be drivenin low pressure conditions such as highlands.

Twenty-Fourth Modification

Each of the conductors 82 equipped with a stack of a plurality ofinsulating layers may be designed to have at least one of a linearexpansion coefficient and the degree of adhesion strength differentbetween an outer one and an inner one of the insulating layers. Theconductors 82 in this modification are illustrated in FIG. 52.

In FIG. 52, the conductor 82 includes a plurality of (four in thedrawing) wires 181, the outer coated layer 182 (i.e., an outerinsulating layer) with which the wires 181 are covered and which is madeof, for example, resin, and the intermediate layer 183 (i.e., anintermediate insulating layer) which is disposed around each of thewires 181 within the outer coated layer 182. Each of the wires 181includes the conductive portion 181 a made of copper material and theconductor-coating layer (i.e., an inner insulating layer) made ofelectrical insulating material. The outer coated layer 182 serves toelectrically insulate between phase-windings of the stator winding. Eachof the wires 181 is preferably made of a collection of conductivemembers or fibers.

The intermediate layer 183 has a linear expansion coefficient higherthan that of the coated layer 181 b, but lower than that of the outercoated layer 182. In other words, the linear expansion coefficient ofthe conductor 82 is increased from an inner side to an outer sidethereof. Typically, the outer coated layer 182 is designed to have alinear expansion coefficient higher than that of the coated layer 181 b.The intermediate layer 183, as described above, has a linear expansioncoefficient intermediate between those of the coated layer 181 b and theouter coated layer 182 and thus serves as a cushion to eliminate a riskthat the inner and outer layers may be simultaneously broken.

Each of the wires 181 of the conductor 82 has the conductive portion 181a and the coated layer 181 b adhered to the conductive portion 181 a.The coated layer 181 b and the intermediate layer 183 are also adheredtogether. The intermediate layer 183 and the outer coated layer 182 areadhered together. Such joints have a strength of adhesion decreasingtoward an outer side of the conductor 82. In other words, the strengthof adhesion between the conductive portion 181 a and the coated layer181 b is lower than that between the coated layer 181 b and theintermediate layer 183 and between the intermediate layer 183 and theouter coated layers 182. The strength of adhesion between the coatedlayer 181 b and the intermediate layer 183 may be higher than oridentical with that between the intermediate layer 183 and the outercoated layers 182. Usually, the strength of adhesion between, forexample, two coated layers may be measured as a function of a tensilestrength required to peel the coated layers away from each other. Thestrength of adhesion of the conductor 82 is selected in the above way tominimize the risk that the inner and outer layers may be broken togetherarising from a temperature difference between inside and outside theconductor 82 when heated or cooled.

Usually, the heat generation or temperature change in the rotatingelectrical machine results in copper losses arising from heat from theconductive portion 181 a of the wire 181 and from an iron core. Thesetwo types of loss result from the heat transmitted from the conductiveportion 181 a in the conductor 82 or from outside the conductor 82. Theintermediate layer 183 does not have a heat source. The intermediatelayer 183 has the strength of adhesion serving as a cushion for thecoated layer 181 b and the outer coated layer 182, thereby eliminatingthe risk that the coated layer 181 b and the outer coated layer 182 maybe simultaneously broken. This enables the rotating electrical machineto be used in conditions, such as in vehicles, wherein a resistance tohigh pressure is required, or the temperature greatly changes.

In addition, the wire 181 may be made of enamel wire with a layer (i.e.,the coated layer 181 b) coated with resin, such as PA, PI or PAI.Similarly, the outer coated layer 182 outside the wire 181 is preferablymade of PA, PI, and PAI and has a large thickness. This minimizes a riskof breakage of the outer coated layer 182 caused by a difference inlinear expansion coefficient. Instead of use of PA, PI, PAI to make theouter coated layer 182 having a large thickness, material, such as PPS,PEEK, fluorine, polycarbonate, silicon, epoxy, polyethylene naphthalate,or LCP which has a dielectric permittivity lower than that of PI or PAIis preferably used to increase the conductor density of the rotatingelectrical machine. The use of such resin enhances the insulatingability of the outer coated layer 182 even when it has a thicknesssmaller than or equal to that of the coated layer 181 b and increasesthe occupancy of the conductive portion. Usually, the above resin hasthe degree of electric permittivity higher than that of an insulatinglayer of enamel wire. Of course, there is an example where the state offormation or additive results in a decrease in electric permittivitythereof. Usually, PPS and PEEK is higher in linear expansion coefficientthan an enamel-coated layer, but lower than another type of resin andthus is useful only for the outer of the two layers.

The strength of adhesion of the two types of coated layers arrangedoutside the wire 181 (i.e., the intermediate insulating layer and theouter insulating layer) to the enamel coated layer of the wire 181 ispreferably lower than that between the copper wire and the enamel coatedlayer of the wire 181, thereby minimizing a risk that the enamel coatedlayer and the above two types of coated layers are simultaneouslybroken.

In a case where the stator is equipped with a water cooling mechanism, aliquid cooling mechanism, or an air cooling mechanism, thermal stress orimpact stress is thought of as being exerted first on the outer coatedlayers 182. The thermal stress or the impact stress is decreased bypartially bonding the insulating layer of the wire 181 and the above twotypes of coated layers together even if the insulation layer is made ofresin different from those of the above two types of coated layers. Inother words, the above described insulating structure may be created byplacing a wire (i.e., an enamel wire) and an air gap and also arrangingfluorine, polycarbonate, silicone, epoxy, polyethylene naphthalate, orLCP. In this case, adhesive which is made from epoxy, low in electricpermittivity, and also low in linear expansion coefficient is preferablyused to bond the outer coated layer and the inner coated layer together.This eliminates breakage of the coated layers caused by friction arisingfrom vibration of the conductive portion or breakage of the outer coatedlayer due to the difference in linear expansion coefficient as well asthe mechanical strength.

The outermost layer which serves to ensure the mechanical strength orsecurement of the conductor 82 having the above structure is preferablymade from resin material, such as epoxy, PPS, PEEK, or LCP which is easyto shape and similar in dielectric constant or linear expansioncoefficient to the enamel coated layer, typically in a final process fora stator winding.

Typically, the resin potting is made using urethane or silicon. Suchresin, however, has a linear expansion coefficient approximately twicethat of other types of resin, thus leading to a risk that thermal stressis generated when the resin is subjected to the resin potting, so thatit is sheared. The above resin is, therefore, unsuitable for use whererequirements for insulation are severe and 60V or more. The finalinsulation process to make the outermost layer using injection mouldingtechniques with epoxy, PPS, PEEK, or LCP satisfies the aboverequirements.

Other modifications will be listed below.

The distance DM between a surface of the magnet unit 42 which faces thearmature and the axial center of the rotor in the radial direction maybe selected to be 50 mm or more. For instance, the distance DM, asillustrated in FIG. 4, between the radial inner surface of the magnetunit 42 (i.e., the first and second magnets 91 and 92) and the center ofthe axis of the rotor 40 may be selected to be 50 mm or more.

The small-sized slot-less structure of the rotating electrical machinewhose output is several tens or hundreds watt is known which is used formodels. The inventors of this application have not seen examples wherethe slot-less structure is used with large-sized industrial rotatingelectrical machines whose output is more than 10 kW. The inventors havestudied the reason for this.

Modern major rotating electrical machines are categorized into four maintypes: a brush motor, a squirrel-cage induction motor, a permanentmagnet synchronous motor, a reluctance motor.

Brush motors are supplied with exciting current using brushes.Large-sized brush motors, therefore, have an increased size of brushes,thereby resulting in complex maintenance thereof. With the remarkabledevelopment of semiconductor technology, brushless motors, such asinduction motors, have been used instead. In the field of small-sizedmotors, a large number of coreless motors have also come on the marketin terms of low inertia or economic efficiency.

Squirrel-cage induction motors operate on the principle that a magneticfield produced by a primary stator winding is received by a secondarystator core to deliver induced current to bracket-type conductors,thereby creating magnetic reaction field to generate torque. In terms ofsmall-size and high-efficiency of the motors, it is inadvisable that thestator and the rotor be designed not to have iron cores.

Reluctance motors are motors designed to use a change in reluctance inan iron core. It is, thus, inadvisable that the iron core be omitted inprinciple.

In recent years, permanent magnet synchronous motors have used an IPM(Interior Permanent Magnet) rotor.

Especially, most large-sized motors use an IPM rotor unless there arespecial circumstances.

IPM motors has properties of producing both magnet torque and reluctancetorque. The ratio between the magnet torque and the reluctance torque istimely controlled using an inverter. For these reasons, the IMP motorsare thought of as being compact and excellent in ability to becontrolled.

According to analysis by the inventors, torque on the surface of a rotorproducing the magnet torque and the reluctance torque is expressed inFIG. 53 as a function of the distance DM between the surface of themagnet unit which faces the armature and the center of the axis of therotor, that is, the radius of a stator core of a typical inner rotorindicated on the horizontal axis.

The potential of the magnet torque, as can be seen in the followingequation (eq1), depends upon the strength of magnetic field created by apermanent magnet, while the potential of the reluctance torque, as canbe seen in the following equation (eq2), depends upon the degree ofinductance, especially, on the q-axis.

The magnet torque=k·Ψ·Iq  (eq 1)

The reluctance torque=k·(Lq−Ld)·Iq·Id  (eq2)

Comparison between the strength of magnetic field produced by thepermanent magnet and the degree of inductance of a winding using thedistance DM shows that the strength of magnetic field created by thepermanent magnet, that is, the amount of magnetic flux Ψ is proportionalto a total area of a surface of the permanent magnet which faces thestator. In case of a cylindrical stator, such a total area is acylindrical surface area of the permanent magnet. Technically speaking,the permanent magnet has an N-pole and an S-pole, the amount of magneticflux Ψ is proportional to half the cylindrical surface area. Thecylindrical surface area is proportional to the radius of thecylindrical surface and the length of the cylindrical surface. When thelength of the cylindrical surface is constant, the cylindrical surfacearea is proportional to the radius of the cylindrical surface.

The inductance Lq of the winding depends upon the shape of the ironcore, but its sensitivity is low and rather proportional to the squareof the number of turns of the stator winding, so that it is stronglydependent upon the number of the turns. The inductance L is expressed bya relation of L=μ·N{circumflex over ( )}2×S/δ where p is permeability ofa magnetic circuit, N is the number of turns, S is a sectional area ofthe magnetic circuit, and δ is an effective length of the magneticcircuit. The number of turns of the winding depends upon the size ofspace occupied by the winding. In the case of a cylindrical motor, thenumber of turns, therefore, depends upon the size of space occupied bythe winding of the stator, in other words, areas of slots in the stator.The slot is, as demonstrated in FIG. 54, rectangular, so that the areaof the slot is proportional to the product of a and b where a is thewidth of the slot in the circumferential direction, and b is the lengthof the slot in the radial direction.

The width of the slot in the circumferential direction becomes largewith an increase in diameter of the cylinder, so that the width isproportional to the diameter of the cylinder. The length of the slot inthe radial direction is proportional to the diameter of the cylinder.The area of the slot is, therefore, proportional to the square of thediameter of the cylinder. It is apparent from the above equation (eq2)that the reluctance torque is proportional to the square of current inthe stator. The performance of the rotating electrical machine,therefore, depends upon how much current is enabled to flow in therotating electrical machine, that is, depends upon the areas of theslots in the stator. The reluctance is, therefore, proportional to thesquare of the diameter of the cylinder for a cylinder of constantlength. Based on this fact, a relation of the magnetic torque and thereluctance torque with the distance DM is shown by plots in FIG. 53.

The magnet torque is, as shown in FIG. 53, increased linearly as afunction of the distance DM, while the reluctance torque is increased inthe form of a quadratic function as a function of the distance DM. FIG.53 shows that when the distance DM is small, the magnetic torque isdominant, while the reluctance torque becomes dominant with an increasein diameter of the stator core. The inventors of this application havearrived at the conclusion that an intersection of lines expressing themagnetic torque and the reluctance torque in FIG. 53 lies near 50 mmthat is the radius of the stator core. It seems that it is difficult fora motor whose output is 10 kW and whose stator core has a radius muchlarger than 50 mm to omit the stator core because the use of thereluctance torque is now mainstream. This is one of reasons why theslot-less structure is not used in large-sized motors.

The rotating electrical machine using an iron core in the stator alwaysfaces a problem associated with the magnetic saturation of the ironcore. Particularly, radial gap type rotating electrical machines has alongitudinal section of the rotating shaft which is of a fan shape foreach magnetic pole, so that the further inside the rotating electricalmachine, the smaller the width of a magnetic circuit, so that innerdimensions of teeth forming slots in the core become a factor of thelimit of performance of the rotating electrical machine. Even if a highperformance permanent magnet is used, generation of magnetic saturationin the permanent magnet will lead to a difficulty in producing arequired degree of performance of the permanent magnet. It is necessaryto design the permanent magnet to have an increased inner diameter inorder to eliminate a risk of generation of the magnetic saturation,which results in an increase size of the rotating electrical machine.

For instance, a typical rotating electrical machine with a distributedthree-phase winding is designed so that three to six teeth serve toproduce a flow of magnetic flux for each magnetic pole, but encounters arisk that the magnetic flux may concentrate on a leading one of theteeth in the circumferential direction, thereby causing the magneticflux not to flow uniformly in the three to six teeth. For instance, theflow of magnetic flux concentrates on one or two of the teeth, so thatthe one or two of the teeth in which the magnetic saturation isoccurring will move in the circumferential direction with rotation ofthe rotor, which may lead to a factor causing the slot ripple.

For the above reasons, it is required to omit the teeth in the slot-lessstructure of the rotating electrical machine whose distance DM is 50 mmor more to eliminate the risk of generation of the magnetic saturation.The omission of the teeth, however, results in an increase in magneticresistance in magnetic circuits of the rotor and the stator, therebydecreasing torque produced by the rotating electrical machine. Thereason for such an increase in magnetic resistance is that there is, forexample, a large air gap between the rotor and the stator. The slot-lessstructure of the rotating electrical machine whose distance DM is 50 mmor more, therefore, has room for improvement for increasing the outputtorque. There are numerous beneficial advantages to use the abovetorque-increasing structure in the slot-less structure of rotatingelectrical machines whose distance DM is 50 mm or more.

Not only the outer rotor type rotating electrical machines, but also theinner rotor type rotating electrical machines are preferably designed tohave the distance DM of 50 mm or more between the surface of the magnetunit which faces the armature and the center of the axis of the rotor inthe radial direction.

The stator winding 51 of the rotating electrical machine 10 may bedesigned to have only the single straight section 83 of the conductor 82arranged in the radial direction. Alternatively, a plurality of straightsections 83, for example, three, four, five, or six straight sections 83may be stacked on each other in the radial direction.

For example, the structure illustrated in FIG. 2 has the rotating shaft11 extending outside the ends of length of the rotating electricalmachine 10, but however, may alternatively be designed to have therotating shaft 11 protruding outside only one of the ends of therotating electrical machine 10. In this case, it is advisable that aportion of the rotating shaft 11 which is retained by the bearing unit20 in the cantilever form be located on one of the ends of the rotatingelectrical machine, and that the rotating shaft 11 protrude outside suchan end of the rotating electrical machine. This structure has therotating shaft 11 not protruding inside the inverter unit 60, thusenabling a wide inner space of the inverter unit 60, i.e., the cylinder71 to be used.

The above structure of the rotating electrical machine 10 usesnon-conductive grease in the bearings 21 and 22, but however, mayalternatively be designed to have conductive grease in the bearings 21and 22. For instance, conductive grease containing metallic particles orcarbon particles may be used.

A bearing or bearings may be mounted on only one or both axial ends ofthe rotor 40 for retaining the rotating shaft 11 to be rotatable. Forexample, the structure of FIG. 1 may have a bearing or bearings mountedon only one side or opposite sides of the inverter unit 60 in the axialdirection.

The magnet holder 41 of the rotor 40 of the rotating electrical machine10 has the intermediate portion 45 equipped with the inner shoulder 49 aand the annular outer shoulder 49 b, however, the magnet holder 41 mayalternatively be designed to have the flat intermediate portion 45without the shoulders 49 a and 49 b.

The conductor body 82 a of each of the conductors 82 of the statorwinding 51 of the rotating electrical machine 10 is made of a collectionof the wires 86, however, may alternatively be formed using a squareconductor having a rectangular cross section. The conductor 82 mayalternatively be made using a circular conductor having a circular crosssection or an oval cross section.

The rotating electrical machine 10 has the inverter unit 60 arrangedradially inside the stator 50, but however, may alternatively bedesigned not to have the inverter 60 disposed inside the stator 50. Thisenables the stator 50 to have a radial inner void space in which partsother than the inverter unit 60 may be mounted.

The rotating electrical machine 10 may be designed not to have thehousing 30. In this case, the rotor 40 or the stator 50 may be retainedby a wheel or another part of a vehicle.

While this disclosure has been discussed in terms of the preferredembodiments in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, thisdisclosure should be understood to include all possible embodiments andmodifications to the shown embodiments which can be embodied withoutdeparting from the principle of this disclosure as set forth in theappended claims.

1. A rotating electrical machine comprising: a magnetic field-producingunit equipped with a magnet unit including a plurality of magnetic poleswhose magnetic polarities are arranged alternately in a circumferentialdirection; and an armature which includes a multi-phase armaturewinding, wherein one of the magnetic field-producing unit and thearmature is engineered as a rotor whose rotating shaft is retained by abearing to be rotatable, the armature winding has conductor portionswhich are arranged at a given interval away from each other in thecircumferential direction and face the magnet unit, the armature isdesigned to have conductor-to-conductor members arranged between theconductor portions in the circumferential direction, theconductor-to-conductor members being made from a magnetic material whichmeets a relation of Wt×Bs≤Wm×Br where Wt is a width of theconductor-to-conductor members in the circumferential direction withinone magnetic pole, Bs is a saturation magnetic flux density of theconductor-to-conductor members, Wm is a width of the magnet unitequivalent to one magnetic pole in the circumferential direction, and Bris a remanent flux density in the magnet unit, or alternatively madefrom a non-magnetic material, the armature is alternatively be designednot to have the conductor-to-conductor members disposed between theconductor portions in the circumferential direction, and the magnet unitis magnetically oriented to have an easy axis of magnetization, in aregion located closer to a d-axis that is a center of a magnetic pole,aligned to be more parallel to the d-axis than that in a region locatedcloser to a q-axis that is a boundary between magnetic poles.
 2. Therotating electrical machine as set forth in claim 1, wherein the magnetunit is magnetically oriented to create an arc-shaped magnet-producedmagnetic path in which the easy axis of magnetization is directedparallel or near parallel to the d-axis in the region close to thed-axis and also directed perpendicular or near perpendicular to theq-axis in the region close to the q-axis.
 3. The rotating electricalmachine as set forth in claim 1 wherein the magnet unit includes aplurality of permanent magnets which are arranged in the circumferentialdirection, and wherein each of the permanent magnets is shaped to havean armature-side outer peripheral surface facing the armature and aq-axis-side outer peripheral surface facing the q-axis in thecircumferential direction, the stator-side outer peripheral surface andthe q-axis-side outer peripheral surface functioning as magnetic fluxinput and output surfaces that are magnetic flux acting surfaces intoand from which magnetic flux flows, and wherein the magnetic path iscreated to connect between the stator-side outer peripheral surface andthe q-axis-side outer peripheral surface.
 4. The rotating electricalmachine as set forth in claim 1, wherein the magnet unit is made of aring-shaped magnet that is a circular ring-shaped permanent magnet, andwherein the ring-shaped magnet has defined therein an arc-shapedmagnet-produced magnetic path in which a magnetic orientation isdirected in the radial direction on the d-axis of each magnetic pole anda magnetic orientation is directed in the circumferential direction onthe q-axis between the magnetic poles.
 5. The rotating electricalmachine as set forth in claim 1, wherein the magnetic field-producingunit has a skew structure in which the magnetic poles of the magnet unitwhich are arranged in an axial direction of the rotating shaft andoffset from each other in the circumferential direction, and wherein askew amount from a magnetic pole center line of each of the magneticpoles of the magnet unit in a first circumferential direction isidentical with that in a second circumferential direction opposite thefirst circumferential direction.
 6. The rotating electrical machine asset forth in claim 1, wherein the armature has a skew structure in whichconductor locations of the armature winding for each phase in the axialdirection of the rotating shaft are offset in the circumferentialdirection, and wherein a skew amount of each of phase windings of thearmature winding in a first circumferential direction from an energizedphase center line extending in the axial direction is identical withthat in a second circumferential direction opposite the firstcircumferential direction.
 7. The rotating electrical machine as setforth in claim 1, wherein the rotating shaft is retained by theplurality of bearings to be rotatable, and wherein each of the bearingsis offset from an axial center of one of the magnetic field-producingunit and the armature which works as the rotor to one of opposed endsthereof in the axial direction.
 8. The rotating electrical machine asset forth in claim 7, wherein the rotating electrical machine isengineered as an outer-rotor type rotating electrical machine in whichone of the magnetic field-producing unit and the armature which works asthe rotor is arranged on a radially outer side, wherein the magneticfield-producing unit includes a magnet holder which retains the magnetunit, and wherein the magnet holder has an overhang which extends in aradial direction of the magnetic field-producing unit, the overhangbeing equipped with a contact avoider which extends in the axialdirection and avoids a physical contact with the armature.
 9. Therotating electrical machine as set forth in claim 7, wherein therotating electrical machine is engineered as an outer-rotor typerotating electrical machine in which one of the magnetic field-producingunit and the armature which works as the rotor is arranged on a radiallyouter side, further comprising a bearing retainer which surrounds therotating shaft and retains the bearings, a housing disposed to surroundthe magnetic field-producing unit and the armature, and an armatureholder which is disposed radially inside the armature to retain thearmature, and wherein the bearing retainer is secured to a first end ofthe housing which is opposed to a second end of the housing through themagnetic field-producing unit in the axial direction, and the second endof the housing and the armature holder are joined together.
 10. Therotating electrical machine as set forth in claim 7, wherein thebearings have a non-conductive grease.
 11. The rotating electricalmachine as set forth in claim 1, wherein the armature includes aring-shaped base member which is disposed integrally with the armaturewinding and secured to an armature holder, and wherein the armaturewinding is covered with a molding material along with the base member.12. The rotating electrical machine as set forth in claim 11, whereinthe base member is arranged radially inside or outside the armaturewinding on an opposite side of the armature winding to the magnet unit,and wherein the base member has a surface which faces the armaturewinding and on which concavities and convexities are formed successivelyin at least one of the circumferential direction and the axial directionto define recesses (151, 152) filled with the molding material.
 13. Therotating electrical machine as set forth in claim 11, wherein the basemember is designed as an armature core made of a plurality of steelplates stacked on each other in the axial direction of the rotatingshaft, and wherein each of the steel plates has an end which faces thearmature winding and has a cross-section tapered in a thickness-wisedirection thereof.
 14. The rotating electrical machine as set forth inclaim 11, wherein the base member is implemented by an armature coremade from a conductive material, and wherein an insulating layer isdisposed between the armature winding and the armature core.
 15. Therotating electrical machine as set forth in claim 11, wherein the basemember has holes which extend in the axial direction of the rotatingshaft and are filled with the molding material.
 16. The rotatingelectrical machine as set forth in claim 11, wherein the armaturewinding is covered with the molding material except portions in an axialand a radial directions thereof.
 17. The rotating electrical machine asset forth in claim 11, wherein the armature holder is made from carbonfiber reinforced plastic.
 18. The rotating electrical machine as setforth in claim 1, further comprising a power converter which includesswitches and is electrically connected to the armature winding, and acontroller which controls on-off operations of the switches to energizethe armature winding, wherein the controller sets a switching frequencyfor the switches in a low current range in which a lower electricalcurrent flows through the armature winding to be higher than that in ahigh current range which is higher in electrical current than the lowcurrent range and in which a higher electrical current flows through thearmature winding.
 19. A rotating electrical machine comprising: amagnetic field-producing unit equipped with a magnet unit including aplurality of magnetic poles whose magnetic polarities are arrangedalternately in a circumferential direction; and an armature whichincludes a multi-phase armature winding, wherein one of the magneticfield-producing unit and the armature is engineered as a rotor whoserotating shaft is retained by bearings to be rotatable, the rotatingshaft is retained by the plurality of bearings to be rotatable, and eachof the bearings is offset from an axial center of one of the magneticfield-producing unit and the armature which works as the rotor to one ofopposed ends thereof in the axial direction.
 20. A rotating electricalmachine comprising: a magnetic field-producing unit equipped with amagnet unit including a plurality of magnetic poles whose magneticpolarities are arranged alternately in a circumferential direction; andan armature which includes a multi-phase armature winding, wherein oneof the magnetic field-producing unit and the armature is engineered as arotor whose rotating shaft is retained by bearings to be rotatable, thearmature includes a ring-shaped base member which is disposed integrallywith the armature winding and secured to an armature holder, and thearmature winding is covered with a molding material along with the basemember.